Pit of The Chimera boss bug

So casually doing chimera boss when he became close to 1hp and did his untargetable hounds dashing attacks on repeat non-stop and sometimes became targetable for like 0.1 second but could not kill him as he became untargetable again. he is influenced by the shaper but did not get shaper anim, and also maven is in boss fight

I have video if needed.

Just had the same issue but it occurred when the boss was about 1/2 health.

EDIT: Just to help anyone else that sees this...

You have to find the clouds of grey smoke and run through them to 'find' the boss. Depending on your build it can be hard to see them with all the eye candy :)