Levi’s Stadium christened its fourth NFL season Sunday afternoon, and the problems that have plagued the building since its opening in 2014 remain: hot weather, lousy football and empty seats.

Things have gotten so bad that the team, in a statement Monday, acknowledged that it has engaged a stadium architecture firm to “review a number of aspects of the stadium with the goal of enhancing the fan experience … to investigate feasible solutions to address concerns regarding warm weather days, both for the short and long terms.”

Yes, a fix to a $1.3 billion stadium that’s 36 months old.

The 49ers have temperature issues. An ice-cold team coming off a 2-14 season, a lukewarm fan base irritated at being gouged and a blisteringly uncomfortable stadium experience.

It was 87 degrees at game time. That kind of weather not only provides a reason to avoid watching mediocre football, but it portends doom at Levi’s. For those in most of the stadium seats, a warm day means massive discomfort. And, in case you hadn’t noticed, we will surely have more and more warm days.

Given the 49ers’ woes, it’s understandable that the stadium wasn’t full, even on opening day. Though tickets were sold — the pricey personal seat licenses and the tickets were hot stuff back in the glory days under Jim Harbaugh— it wasn’t full at kickoff or during the first half, when the game was still competitive. But many of those who did come had to flee.

I tweeted a picture of the virtually empty east side of the stadium as the second half kicked off. Though photos of Levi’s Stadium’s empty seats are nothing new, this one — perhaps because it was the opener of a “fresh start” season, or because it was so vacant — went viral and was soon trending.

That brings out some craziness. Some accused me of faking the photo, or taking it in the preseason (both incorrect). Some claimed that it was Colin Kaepernick’s fault, and that because the 49ers had employed the lightning rod quarterback, fans were staying away. Others claimed the opposite, that fans are boycotting the team and the NFL in general because it has shunned Kaepernick.

Though those opposing points of view are part of the NFL’s ongoing issues — both fans on the right and on the left are irritated at the league for different reasons — they have little to do with the Levi’s Stadium problem.

The answer is far more simple. It’s a bad team, ripped from its historic roots, playing in a flawed building, charging exorbitant prices.

The shady side of the stadium was full and took in many refugees from the sunny side, but that area accounts for only a relative sliver of seats, below several stories of glassed-in suites. Most of the seats are on the exposed side. And it’s miserable.

Why is it so bad? Are 49ers fans soft, after years of cool Candlestick Park breezes? Why can’t they enjoy 90-plus degrees the way Packers fans revel in minus-9?

No one can explain why it’s so terrible, but it is. Seats the color of Red Hots. A steep angle. Unrelenting sun. Glare off the glass tower. No circulation and no shade anywhere.

Adding to the problem are a terrible team, unbelievably long concession lines and underground air-conditioned bars for the uber-rich to hide in. An embarrassing look.

On Monday, team President Al Guido said the team is aware of the concerns and had tried some things through guest services to alleviate the discomfort, including free water, misters and sunscreen.

In terms of other options, Guido said, “There’s nothing definitive now.”

The 49ers will be working with Populous, a Kansas City, Mo.-based architecture firm.

The Dolphins put in a shade/shelter canopy last year, to the tune of about $78 million. Would the 49ers pay for such an expense for their fans?

Maybe, but there are complications. Levi’s is an enormously tall building, in the flight path of Mineta San Jose International Airport. A canopy would add to the height.

In addition, the team is in litigation with the city of Santa Clara, whose stadium authority owns the building and leases it to the 49ers. Launching and financing any capital improvements may be tricky in such a contentious atmosphere.

The 49ers aren’t alone with attendance problems. Of the myriad issues the NFL faces, a major one is what’s happening with the four franchises in the nation’s most populous state.

The product does not seem to be popular. There is a disconnect between the NFL and Californians.

In addition to empty seats in Santa Clara, the Rams played in a half-empty L.A. Coliseum. The “Los Angeles” Chargers haven’t hosted a home game, but will be playing in a 27,000-seat soccer stadium in suburban Carson that they had trouble filling in the preseason. The Oakland Raiders are headed out of state.

Los Angeles has two teams it didn’t ask for and has little interest in. For a lesson in what Angelenos prefer, look at the crowd at the Coliseum for USC vs. Stanford on Saturday. Then compare the Rams’ opener on Sunday. More than 90,000 squeezed into the Coliseum for the college game. Twenty hours later there were huge swaths of empty seats in the same structure. The announced attendance for the Rams was 60,128 — and that’s with some tickets going for $6 and others being free. But there weren’t nearly that many people there.

The Raiders, after struggling with attendance and competence for years, finally have figured it out on the field. Just in time to high-tail it to the 42nd-ranked television market, where a new stadium will provide no tangible home-field advantage and there’s no particular clamor for the team’s arrival. Las Vegas, here they come.

And then there are the 49ers, who have a modern building and a once-proud team, both desperately in need of fixing.

Ann Killion is a San Francisco Chronicle columnist. Email: akillion@sfchronicle.com Twitter: @annkillion