I've encountered this issue as well, the entire group I recently went with did actually, but this was the first time it's ever been an issue on my end. Every transition that involves the mists taking you somewhere in Sithicus, upon loading, seem to just leave a black screen that so far appears to only be fixed by leaving the game and reentering. Before yesterday I've never encountered this issue with them, they usually loaded up fine, so I'm assuming a more recent update may have complicated it in some way (though whether server related or beamdog related I have no idea).