I tried going back to the dungeon on Skull Island, but when I hit the lever to load the dungeon some enemies spawned inside the door. The enemies were crushed to death but the door to the dungeon was still closed the whole time and now won't open. I've left the dungeon and came back, I've went back to the previous area and came back - the door still won't open. Does anyone know a fix for this?

I haven't arrived there yet, and I don't know. I am writing just to let you know that you are not being ignored. :)

Sorry for a possibly dumb question, but have you tried to move the lever a few times back and forth? I have noticed it in some normal levers, that sometimes they needed to be de-activated and then activated again in order to work.

I tried that. I ended up just reloading an old save and losing an hour or so of progress. The issue didn't reoccur and I was able to finish the game

I think I might actually know what caused this. Earlier in the game a group of spiders followed me into a dungeon entrance. I flipped the lever and they disappeared. Hours later when I flipped the lever to leave the dungeon, the spiders reappeared in the exact same position. I think what happened is an enemy was following me when I went to leave the skull dungeon. When I got back from selling stuff the enemy must have spawned in the same position which was inside the now closed door. The enemy was crushed to death and the loot it dropped might have prevented the door from opening. I left and came back a few times so I feel like the loot should have disappeared by then f that was the issue. I'm still not 100% sure why the door wouldn't open but I'm pretty sure I know how the enemy spawned inside the door. I already saved over the save file where this happened to me so I can't go back to test solutions.