Randomly got Internal Server Error and now i can't get onto the server.

Whenever i try to enter my server i get internal server error, i got this after going into a nether portal. I have already been playing for a few days and have a full inventory + advancements, so i almost can't delete the player data either. Here is my server log! https://mclo.gs/iSceruH Any help would be appreciated

Quote from Joshua

Seems to be due to an entity near you. I'd suggest trying to kill all entities or just regenerating the nether world.

I should have written this a lot better, so basically what happened is that i go into the portal from the overworld into the nether, i walk a bit and then i get to a fortress ( i have already been there ) and right next to the fortress i have another portal cause i am never able to remember the way back to the original portal. When i enter that second portal from the nether to the overworld i remember being in the overworld for a few a seconds working fine, but almost right after i got this error and now i can't get into the world at all but everyone else can. Something else that is pretty weird is that the error kinda changes as 50% of the time i get Internal Server Error and the other 50% i get An existing connection was forcibly closed by the remote host. So the nether probably doesn't have a lot to do with this. And my friend that is able to play went to the portal killed off a few entities surrounding it (wasn't a lot) but it still didn't work.