Root Abyss Boss Mechanics

This has existed since forever, having this suddenly become the cause of the current problems is questionable.

yes, however the fact that due to latency, there's a delay in you moving, and the server recognizing that you moved, would explain why people are getting hit by boss attacks that they already dodged, since it also probably applies to monsters.

so the boss attacks
you get attacked

but you don't get the client notification to play the boss attack until a few seconds later due to lag, and on your screen the boss attacks, but serverside, the attack is already over, and you were just standing there and taking it.