Francisco Alvarez is confident he has pinpointed the cause behind his struggles at the plate.

More than the league adjusting to him throughout his rookie season, Alvarez believes it’s himself that has changed.

The Mets’ 21-year-old catcher — who was the No. 1-ranked prospect in MLB before he was called up earlier this season largely based on the rare power he possesses — had not hit a home run in his past 12 games after hitting four in a four-game span.

During that homer-less stretch, Alvarez slashed a woeful .108/.175/.135 with no RBIs, a .310 OPS, three walks and 12 strikeouts.

In total, Alvarez had just four hits in his previous 40 plate appearances as play began Tuesday.

Manager Buck Showalter sat Alvarez for their game against the Brewers at Citi Field on Tuesday evening — a 7-2 Mets win, instead opting for Omar Narvaez as the starting catcher.

“I don’t think [pitchers] actually made that many adjustments to how they’ve been pitching me. I think it’s just, I’ve been missing a lot,” Alvarez told The Post through team translator Alan Suriel. “I haven’t been coming up with the big hits, but they’ve been executing their pitches. That’s what it comes down to.

“They were executing them before, but I was able to take advantage of them better.”

Specifically, Alvarez pointed to his hips as what’s most gone awry.

He’s opening up too quickly, Alvarez said, with the lower half of his body moving faster than the upper half and resulting in him lunging at pitches.

Along with hitting coach Jeremy Barnes, Alvarez has focused on staying planted in the box, which comes with trusting his hand speed to catch up to the high-velocity pitches he likely didn’t see in the minors.

But Alvarez, who’s leaned on Francisco Lindor as a mentor during this rough patch, hasn’t let his hitting woes affect his defense.

The biggest question mark in his game when the Mets called him up, Alvarez’s defense behind the plate has been a pleasant surprise and he has consistently been lauded by the team’s pitching staff.

“I feel like when I’m there, paired up with Max [Scherzer] or Justin [Verlander] or even [Carlos] Carrasco, I need to be able to separate my offense from my defense,” Alvarez said. “When I put my equipment on, when I put my shin guards on, I take a deep breath and say, ‘All right, we’ve got to focus in on the game right now, on the game plan.’

“That’s how I’ve been able to do it.”