Essence monsters attacking and moving while "trapped"

A group of essence monsters was actively attacking and even moving for short distances while still trapped by crystals.

I could not hit them but they could hit me, and nearly got killed when first encountering them.

Here's a little video of the event after I isolated them:
https://youtu.be/So1h-e-xDE8

Main monster has a fair bit of modifiers, not sure if any of those or some combination could have caused this.

After recording, I was able to free them and kill them the usual way, just getting hit once or twice while freeing them.