I've run into a couple fps and ops where the boss has not shown up on my screen (of the specific times I can recall, HM False Emperor - Malgus, HM Maelstrom Prison - Lord Vantharast, SM EV - Soa). It doesn't happen consistently and sometimes the boss will come back, so I'm not sure what's setting it off. When I can target him through another player's target I get "too far away" error messages even if I'm right in the middle of the melee group, and my toon appears to be aiming her blaster rifle at the floor.
Has anyone found any fixes or workarounds for this?
For Malgus, yes. You need to use two knockbacks on top of each other (same way you kill him) where you think he is. He pops back out of the floor and you can kill him normally.
Only saw that once on Soa ( he was 100 meters above the raid during a damage phase) and we just jumped off a cliff instead of bothering with it.