So while in act 3, I've encountered a bug with the Ravengard questline.
Here are all my plotflags surrounding the specific quest:

1. Had Wyll brake the contract with Mizora, meaning Ravengard would die.
2. Found the Iron Throne, and managed to save Ravengard even though Mizora sent exploding spiders after him (dimension door ftw!). He was the first in my party to go into the sub, and eventually 3 of my party also got in the sub, while Astarion died. Ravengard said he'd meet me at camp. Also saved the mindflayer, and most of the other prisoners.
3. Was ambushed by the Sea followers when exiting the submarine, and choose to protect the submarine dwarf. I defeated all the Sea followers, the dwarf lived through the fight, and while no other convo triggered, I was able to walk up to him for (i believe) a line or two of dialogue? Not sure anymore. However, the questlog updated to say he didn't survive.
4. Used Withers to ressurrect Astarion, then went for a long rest
5. Got a convo with Mizora where she 'congratulates' me for saving Ravengard
6. Wyll says that his father will be waiting for us at camp
7. However, Ravengard didn't show up. I continued playing and blew up the steel watch forge, took another long rest, and still no Ravengard.
8. Returned to the submarine, thinking maybe I could talk to him there, but I cannot enter the submarine again since "It's broken", and the dwarf is also nowhere to be found. The mindflayer did register correctly, and I got to talk to him and he gave me a reward.

So I'm scared it's a bug, and Ravengard (and the dwarf?) are lost in this playthrough.
Hope this helps!