Ultimatum Boss becomes invulnerable after parry (video)

Here is the bug in the video:
https://www.youtube.com/watch?v=3LP0nvrifgY&t=113s

In the end I showed that my character has 100% accuracy.

Also, earlier in the video, I somehow got a parry debuff on myself:
https://www.youtube.com/watch?v=3LP0nvrifgY&t=18s