I'd say for around a week now, players having been vanishing at world bosses about half way through the fight, basically turning them into invisible walls because collision is still enabled. It even just happened at vell and all of the ships vanished as well. 

Picture at Garmoth today

Died getting stuck on invisible people three times at nouver, luckily didn't lose any crystals.

Another bug would be this, nouver keeping his bloodstorm effect after the cast is already over. Causing severe visiblity issues.

This image was taken a week prior to the invisible issue.

There is a setting allowing to hide other players if your PC is struggling, have you enabled it ?

This setting just hides characters but collisions still happen.