Titan Grotto Boss bugged/can't be killed

After the update it appears the boss is bugged made new characters and my group and I get to a certain point in the fight, sometimes a quarter health sometimes half and then we just cease to do damage, all attacks go right through him and you see no damage at the top bar... Restarted the instances multiple times and same result.

gg just happened to me

Just tried it again and it looks like the hitbox is just in the wrong place
and was moving around like crazy but i can do damage once i found it

Same shit happende to me on hcssf with a monk in act 2. What now?

This is happening again, just went a solid minute not being able to deal damage.