For the past month, Fitbit remained silent while customer complaints mounted over a recent software update for its Charge 2 fitness tracker that ruined some devices.

But on Tuesday, in the wake of a CBC News investigation, the San Francisco-based wearable technology company acknowledged there's a problem.

"We have determined that a recent firmware update is affecting the performance of a very small subset of our older Charge 2 devices," said Fitbit in an email.

The company makes wireless fitness monitors that calculate daily activity such as walking steps and other health indicators, such as heart rate.

Following the rollout of a Charge 2 software update on July 24, customer concerns began mounting on social media and Fitbit's online community forum, which has received more than 150 complaints.

Common gripes included the update destroyed the tracker or prevented its internal battery from holding a charge.

<a href="https://twitter.com/fitbit?ref_src=twsrc%5Etfw">@fitbit</a> <a href="https://twitter.com/FitbitSupport?ref_src=twsrc%5Etfw">@FitbitSupport</a> when will you be fixing the update thats causing everyones trackers to stop working? Mine will not connect at all and now the watch doesn't even turn on. —@here4thetree That firmware update has killed so many trackers. And the company seems to not give a crap. So sad. So annoying. So greedy. —@pantsdancelol

Michelle Hals of Minneapolis said her Charge 2's battery took a fatal hit after she downloaded the update a couple of weeks ago.

She said she's surprised by Fitbit's latest acknowledgment because, until now, the company hadn't addressed customer complaints.

"All along from the community forum, and from my interactions with them, they have never once even given an inkling that it might be their fault," said Hals. "They just buried their head in the sand."

We're on it

Fitbit told CBC News it's currently tackling the problem.

"We are committed to working closely with each customer to identify the source of any issues and ensure satisfactory resolution," it said.

"The vast majority of users have successfully implemented the update without issue."

The company didn't offer any hard numbers of affected customers, or an explanation of how the software update impaired some trackers.

Now discontinued, Charge 2 retailed for between $160 and $200, according to customers.

Fitbit make wireless fitness devices that monitor health measures such as heart rate, and record daily activity like walking steps. (Mark Lennihan/Associated Press)

Fitbit has carved out a loyal following in the booming fitness tracker market, selling close to 14 million wearable devices in 2018. But issues with the Charge 2 update have tested the loyalty of some customers who say they're not impressed with how the company handled their case.

"They're working on a satisfactory resolution only after the press caught wind of this issue," said Sunny Malhi of Edmonton.

He said that after downloading the software update for his Charge 2 Fitbit a couple of weeks ago, it immediately died.

"It can't read the time, it can't read the steps, battery runs out within an hour."

According to an online chat transcript with Fitbit, Malhi told the company on Aug. 22 that the problem is widespread and he believed it was triggered by the latest software update.

Fitbit didn't address his concerns and offered him a 25 per cent discount on a new tracker, because his one-year warranty had expired.

"This is not normal wear and tear," Malhi told CBC. "It's an issue caused by their programming engineers, so warranty should not apply to this."

Sunny Malhi of Edmonton said his Charge 2 Fitbit died following the software update. Now the screen only shows the battery icon. (submitted by Sunny Mahli)

Hals was also unhappy when Fitbit offered her a 25 per cent discount after she complained about the demise of her device.

"That's a completely unacceptable solution," she told the company in a Twitter message on Sunday. "Your firmware update messed up my tracker. You are responsible to make it right."

The company didn't respond to her accusation, replying, "Great tweeting with you!"

Michelle Hals of Minneapolis was disappointed when Fitbit would offer her only a 25 per cent discount on a new device after she said a software update made her tracker useless. (Michelle Hals/Twitter)

Bob Lai, a Vancouver customer, got a much better offer — a new Fitbit. But it came after he informed the company that he had been in touch with the media.

When Lai first complained to Fitbit that the software update had ruined his Charge 2, he was offered a 25 per cent discount on Aug. 23.

He rejected it. "Twenty-five per cent is kind of like a slap in the face," Lai told CBC.

On Saturday, he emailed Fitbit again, and this time included an email address he found for a vice-president with the company.

Lai also informed Fitbit that CBC News had reached out to him and he was in the process of contacting other media.

The next day, the company said it would send him a new Fitbit as compensation.

"I don't it think it should take me escalating [it] all the way up to their VP and contacting media … for me to get a replacement," said Lai.

CBC News asked Fitbit if it now plans to offer new trackers to all affected customers.

The company responded it's working with customers who come forward, on a case-by-case basis.

After learning from CBC that Fitbit is now addressing the problem, Hals made another plea to the company on Thursday. This time, she was offered a new tracker.

"What took them so long?" said Hals who still has concerns about how it all played out. "When the new one dies, I'll get a new tracker, but it will not be a Fitbit."

Other models affected?

CBC News also interviewed a couple of Fitbit customers who own other models. They too said the recent software update had negatively impacted their device.

Hildo Garcia of Austin, Texas, said his Flex 2 tracker died following an update issued a couple of weeks ago.

"It does not light up, it doesn't do anything. It just gets hot."

Hildo Garcia of Austin, Texas, said his Flex 2 Fitbit was ruined following the software update a couple of weeks ago. (submitted by Hildo Garcia)

Garcia complained to Fitbit by email last week, and protested when he was offered a 25 per cent discount.

"I think it was wrong," he said.

Fitbit told CBC News that Garcia's problem is likely an unrelated issue and the company would happily work with him on a resolution.

But Garcia has already bought a new fitness tracker from a different company.

"I don't trust them anymore," he said.