Boss disappearing in mid-fight?

When I was doing hydra earlier in DF I heard a healer complained about hydra disappearing on his client and he couldn't dodge fear itself, I thought it was just a lame excuse.

But later when I solo tanked garuda HM, towards the end of the fight, garuda never returned on my screen after teleported up to summon the 2 sisters... I had her focus targeted (which to my surprise, had its reset issue fixed and stayed up all time) and the focus target bar remained so I could still dodge slipstream, but her character model was just nowhere to be seen, no effects no nothing, I only get damages poping up my head.

not sure if anyone else having this issue or it's just the new nvidia driver?

There's always been an issue with Garuda not coming back afterwards. Not sure of the Hydra one, never had that happen.

I've had it happen on Titan. My PC was on for too long (usually after 8 or so hours my game will crash to desktop when trying to teleport to or from a heavily populated area.) That same amount of time had passed in this case too.

After wiping and reviving I noticed a massive frame rate drop when my screen was loading us back to the beginning of the arena. Titan failed to load on screen during this brief lag event. Though tanking his targeting circle made him even easier since you could see his abilities on the ground more clearly.