Hello there!
Firstly;
Have you tried resetting your characters locations? You can do this through
User Panel > Reset Location on each of the characters you can't go on.
How is this issue going for you, Xenek? All fixed or still having issues?
I could suggest you trying to change Rendering Systems, as both work in different ways, but I'd love to hear an update, maybe you could share what you were doing with FH before you started having these issues? Also, maybe you could tell us which entrance to Seaside Grove you were using? Either through The Grounds or Lonely Cave?
It's a possibility that this could be happening with a number of other players, and you could be the only one reaching out about this issue so far. If this issues is still ongoing, then maybe some maps are due for a quick restart.