When I use the Forest Dungeon Portstone, after a few seconds of loading, I get the Loading Error, "Failed to load: data/Map105.json".
Ah that's a bug. That item is not supposed to be in the public build. Can you say where you found it?
I don't remember finding it, I just noticed it was suddenly in my Key Items. Based on the last time I looked there and didn't see it, it had to have happened somewhere in the forest area. I first noticed it after beating Wulfrick.