Facebook Chief Operating Officer Sheryl Sandberg speaks on stage during Facebook session at the Cannes Lions 2019 : Day Three on June 19, 2019 in Cannes, France.

"We remain focused on requiring authenticity and transparency for ads that may influence public opinion around elections," she said.

A Facebook spokeswoman said the company doesn't provide data on its ad enforcement, but said it is always working to refine its approach and improve overall.

This comes as Facebook pushes hard for the dollars of small businesses, which now have increasingly sophisticated ad offerings from companies like Snapchat , Google and other platforms that are making it easier for smaller players to advertise online. At the Cannes Lions International Festival of Creativity in France last week, Facebook chief operating officer Sheryl Sandberg characterized Facebook's ad platform as a means of equalizing big and small advertisers.

Flagged ads can end up in limbo as they await human review, sometimes taking days to get approval, they said. Small business advertisers said they were particularly affected by the political ad filter since ads are often flagged automatically and they often don't often have quick access to a human reviewer to appeal to.

But advertisers say the changes Facebook made to its artificial intelligence system does more than just flag political ads. Many ads that mention social issues (like marketing for "eco-friendliness") get caught in Facebook's digital net, even if they're not outright advocating for a cause, advertisers said. CNBC spoke to eight advertisers who have encountered various issues with flagging. Many of them characterized the system as overly broad and confusing.

Spillane's experience running ads for small businesses isn't uncommon these days. Since the Cambridge Analytica scandal broke in 2018, Facebook has made a number of changes purporting to make it harder for bad actors to place ads and influence elections. The company rolled out an archive of ads last year so consumers can see who's spending and how much on ads for politics and other issues.

He said he decided to become verified to run political ads to prevent future issues just in case.

"We weren't talking about anything that could have been controversial, we were stating some of the values … Not trying to get involved in the Green New Deal or anything like that," Spillane said in an interview with CNBC. "That ad was actually flagged, not approved and never was able to run."

It turns out Facebook's ads manager system had flagged Spillane's paint ad because it determined it was a political or issues-based ad, which requires an extra level of approval to publish on the platform.

The ad seemed innocent enough, until Spillane received a response from Facebook that his ad had been flagged and couldn't run without verification that he had U.S. identification documents and a domestic mailing address.

Earlier this year, Wil Spillane, a social media strategist at Delaware-based Trellist Marketing and Technology, tried to post a Facebook ad for a client that made a chemical ingredient for paint. He said the ad positioned the product as eco-friendly because customers would only have to use one coat of paint, thus reducing their carbon footprint.

Facebook has a list of "prohibited" content in its advertising policies that spans 30 sections, banning ads on everything from the sale of body parts to payday loans. When it comes to ads about social issues, elections or politics, Facebook says it can restrict those ads, and any advertiser running ads on those topics (except for news publishers identified by Facebook, it says) must complete an authorization process that proves they're based in the U.S.

The list of social issues that can be considered to require advertiser authorization and labeling in the U.S. is extensive. It spans hot-button issues like abortion and terrorism, but also includes seemingly less divisive issues, like the environment, health or education. The company said it doesn't mean a mere mention of those topics will be flagged, but they could be if a post involves discussion, debate or advocacy of a topic. The policy pertains to ads with "content that takes a position on or advocates for or against social issues."

A Facebook spokeswoman said the policy was "broad" when it was announced in 2018 as it sought to improve and refine enforcement and listen to feedback over time.

Facebook, on its Ad Library report for the U.S., claims advertisers have spent more than $650 million on ads about social issues, election or politics since May 2018. That figure includes spend on an ad for a product called a "TreeDiaper" that absorbs rainwater and irrigation water for plants, and one for a free (just pay shipping!) "Poop Emoji Farting Plush Toy." (A Facebook spokeswoman said the poop emoji toy shouldn't have been marked as political, while the TreeDiaper was flagged as a "social issue" because part of its marketing claims involve saving the environment).

With those rules, everything from the "TreeDiaper," which says it aims to help conserve water, to ads that involve charitable giving with a purchase, can get caught up.

Facebook said it's working to clarify its definitions of "social issues," including "environment, where benefit of purchase speaks to being good for the environment."

"This alone, without further discussion, advocacy or debate should not require these product and transparency elements in the future," a spokeswoman said.

Facebook says it reviews all ads through a combination of artificial intelligence and human review, but the spokeswoman said that the system is "mostly automated," along with humans that support that review. Facebook said it checks an ad's images, text and positioning as well as content on an ad's landing page for community standards and advertising policies. Ads that are already running also might be flagged by artificial intelligence or reported by users.

If an ad is rejected for not complying with policies, the site says it sends the advertiser an email explaining why. Advertisers are prompted to either edit their ad or appeal the decision.

Sam Kessenich, chief digital officer at RyTech, recently tweeted about his troubles when he was trying to run a spot about shoes. Tweeting at Facebook's ads account on Twitter, he said: "I'm just trying to market shoes for a client. Not sure how my ads are being construed as 'political/of national importance' but your lack of response for over a week now definitely isn't clearing anything up."

Kessenich said he's experienced issues both with new spots and spots that were running fine for months then suddenly flagged without even having changed them. What's more, he's had some identical ads where one might be flagged and the other isn't.

Big advertisers often have a dedicated Facebook representative they can call to push campaigns through or help explain why an ad is being flagged. Those who spend less say they have less personalized attention.

But they still need Facebook.

Tamara MacDuff, a small business mentor at the nonprofit SCORE, said Facebook's targeting capabilities have been crucial for small businesses in the digital age.

"Facebook is still the number one platform for a lot of small businesses," she said. "It allows them to connect with people and level the playing field with some of the bigger brands. They still can't compete in the same space as Procter & Gamble, but they can come a little bit closer."

She said she encourages businesses to do things like also provide content in addition to paid ads just in case they have issues with paid ads.

SCORE's director of communications and public relations Betsy Dougert has had various problems of her own with Facebook's flagging of content. The organization is hosting a webinar this week called "Facebook is Falling: Crucial Marketing Strategies You Must Activate Now." She said that even though small businesses still can get value out of the platform, not having answers can be a source of frustration.

"There is no one there to talk to you," she said. "There is no phone number to call ... the only human beings I've heard from at Facebook are ad reps trying to sell me things. When you can't get a live human being, it can be really frustrating."

And for businesses that rely on Facebook for marketing, time is everything. If a campaign meant for Father's Day can't run on Father's Day, for example, it stands to miss out on sales as it waits for human review.

Paul Reed, who does marketing for music festivals and clubs, said "the flagging process has gotten incredibly aggressive" in the last three months, "way more than it ever was before." Reed's issues with rejected ads have involved issues beyond political flagging, though.

He said changes to algorithms and approval policies seem frequent and not communicated clearly to advertisers.

"It's just a giant guessing game," he said. "Then everyone in the digital space is scrambling. It's like we're trying to solve a puzzle of what do we do now?"

Betsy Hindman, principal at digital marketing firm Hindman Company, said the constant misfires give her little faith that Facebook can actually do things it claims it can do.

"If you think about them saying they're going to make political ads safer, and you think about how incompetent they are at seeing what is a political ad and what isn't, it really makes you realize the extent to which their system can still be abused," she said. "The way they're seeking to get back trust now, it's concerning, because I think they're over promising and people may believe them that they are really that competent."

The Facebook spokeswoman said the company continues to review its political ads policy to "better understand the types of issue ads that require additional transparency to people who use our platform versus ads that fall outside the scope of true discussion, debate or advocacy."

For example, Facebook changed its policy to make sure including a Pride flag wouldn't require extra authorization before it could run, the spokeswoman said.

Valeria Bisceglia, who advises small businesses at the Connecticut Small Business Development Center, said this is a matter of small businesses just learning to better deal with Facebook and becoming as educated as they can be.

"As a small business you're dealing with this huge company," she said. "It happens to the everyday consumer trying to reach customer service in many large companies. Sometimes it's challenging. It requires patience… I think a big part of it is the work that a small business owner can try to do ahead of time to try and prevent the issue to begin with."

She said issues like a business owner having an account flagged because there's a mismatch between their account name and billing name is one pitfall she sees, along with things like having too much text in an ad image. Those issues, though frustrating, are preventable, she said.

"I always recommend to people to take a few minutes to read the guidelines first," she said. "I know it's tedious and nobody wants to do that ... it can help with a lot."