It’s the problem that everyone can identify and yet no one can solve: grotesque third-quarter performances that keep leaving Miami at a loss. The Heat has played four home games this season and has been outscored 137-71 in the third quarter of those games, a big reason why Miami is just 3-3 entering a six-game road trip that begins on Wednesday night in Phoenix (9 p.m., FanDuel Sports Network Sun).

Those momentum-swinging quarters contributed heavily to losses to Orlando and New York and were a factor in Monday’s loss to Sacramento. Miami surged ahead by 13 early in the third, fell behind by nine late in the third, then rallied to lead by five with 1:14 left before losing 111-110 on a Domantas Sabonis rebound and nine-foot floater at the buzzer. “We’ve looked at everything,” coach Erik Spoelstra said of the third-quarter collapses. “At some point, you have to take a stand and say enough is enough with these third quarters. We are going to have to figure it out.. Three straight games where I had to call a first timeout. It takes a little wind out of your sails.” What’s confounding is the Heat has been an above-average team in every other quarter. Miami has outscored opponents by 17 points in the first quarter, 25 points in the second quarter and 17 in the fourth. But Miami has been outscored by 52 in the third. Miami is the NBA’s lowest scoring team in the third quarter.

“It’s like we like to let our foot off the gas and let teams back into it to try to make it interesting,” Bam Adebayo said. “We’ve got to figure out the third quarter. It’s been a deciding factor in a lot of our games.”

Jimmy Butler has a theory for what’s happening: “When we aren’t making shots, that’s normally when teams start to go on runs. We don’t get back, we don’t defensive rebound. It’s a defensive thing, but for us, it’s more offense. When we don’t see that ball going through that basket, mentally we have to be tougher and stronger to still get stops. That’s the main problem; that’s what you’re seeing in the third quarter.” On Monday, the Kings unleashed their third-quarter run while Miami was shooting 6 for 20 and 1 of 8 on threes in the third. The Heat also shot poorly in third quarter meltdowns against Orlando (which outscored Miami 39-18 in the third on opening night), Detroit (26-14) and the Knicks (35-22). Of those four games, Miami won only the Pistons game. The Heat is shooting 38.2 percent overall on three-pointers, which is fifth best in the league, but just 29.5 percent on third-quarter threes. “We need to come out of the half stronger,” Tyler Herro said. “Obviously, it’s been a trend. [We need to] just find a way to be motivated to come out in the second half. Every quarter we won [Monday] except the third.” Is the problem mental at this point? “No,” Adebayo said.

“When we get in that moment, we always have that conversation of, ‘we can’t keep letting this happen.’ For three quarters, we play hard as [expletive] on defense. [But in the] third quarter, we’ve got to figure it out.” All of this could be headed toward a change in the starting lineup; replacing Nikola Jovic with Jaime Jaquez Jr. or Haywood Highsmith would be the simplest move. Shifting Jaquez to the starting group would be easier to accommodate amid the rapid development of second-round pick Pelle Larsson, who essentially took Jaquez’s place and played the final 6:58 against Sacramento.

Jaquez missed the Kings game with a stomach illness. But he’s the oddity about the Heat’s starting lineup, albeit in a small six-game sample size: The lineup is above average when it plays together in the first half but awful when it plays together in the second half. In the third quarter, the Butler, Adebayo, Herro, Terry Rozier, Jovic starting group has been outscored by 28 points in 30 minutes, the worst plus/minus of any of the 722 five-man lineups that have been used by teams in the third quarter of games this season. The Heat’s starting five has been outscored 85-57 in their 30 third quarter minutes as a group. When those five have been on the floor together in the second half overall, they have shot 32.8 percent from the field (21 for 64) and 31.4 percent (11 for 35) on threes. The Heat has played 38 different lineups in the second half of games, and none have been nearly as bad as the starting group.

(The next worst lineup has been outscored by 11 in the second half.) In the first half, the Adebayo/Butler/Herro/Rozier/Jovic quintet has been better than average. The starting group has outscored teams 90-84 in 35 first half minutes. They’ve shot much better on threes (10 for 21, 47.6 percent) when they’re on the court together in the first half than the second half. If the Heat moves toward starting Jaquez or Highsmith in place of Jovic, keep in mind that neither of those lineups has been great, though it’s impossible to make any grand conclusions because of the small sample size.

Since Jaquez entered the league last season, a lineup of Jaquez, Butler, Adebayo, Herro and Rozier has been outscored by nine points in 15 minutes. Including 59 minutes last season and five this season, a lineup of Highsmith, Butler, Adebayo, Herro and Rozier has been outscored by 11 points in 64 minutes. Whatever the solution, Herro said: “There’s not much to talk about at this point except the third quarters. We’ve got to figure it out.”