Zombie Villagers don't shake while healing.

While I was playing in my survival world, I found a group of zombie villagers that I wanted to heal to get some librarian villagers. As they were healing though, they would not shake to indicate that they are getting close to finishing the healing process. This is one of the many bugs introduced within this update(1.16.210)

 

What should happen is that the zombie villagers should start shaking as they get close to finishing the healing process, but what I see is no shaking.