The only thing I can chalk it up to is injury or problems with his orthotic/brace. Jaylon was a MUCH more active and violent player in 2018 than in 19 - and taking on blocks wasn't the issue. He played Mike all year in 2018 and dealt with plenty of guards effectively.
The most visible difference for me was in zone. 2018 Jaylon was awesome in deep zone - a guy catches it underneath him, he explodes forward and pops him for a 4 yard gain. 2019 Jaylon would see the catch, hesitate, stumble around, take a crappy angle, and just get beat 1 on 1. By the time the DBs wrestled that guy down, he'd have a 15 yard gain off a checkdown.
I'll repeat it again - if Jaylon and LVE's problems really were about dealing with blockers, you would have seen them dominate while defending toss plays, RB flareouts, deep zones, etc, when they were playing untouched in space. They roundly sucked at all of those assignments in 2019, and killed them in 2018. So what changed? My only answer is medicals.