I can't find any topics about this problem so maybe I am alone with this problem.
Sometimes, when leaving the Nether I receive the "Internal Server Error" message. Usually this happens after leaving via a second portal that I create in the Nether, but it also just happened via the normal one.
Also, sometimes the portal will work...but clearly behave in an odd way and drop me on the regular world but not at the corresponding nether portal. Instead, it drops me at the coordinates for the portal I entered but on the overworld (so if the portal in the nether was at 10,10 it would drop me at 10,10 in the overworld). This is also where I wind up when I load a map that crashed with the Internal Server Error issue.
I am running:
Villages in more biomes
Multi Page Chest