I encountered same thing in same situation. Spent time between resource gathering in a Mountain Biome and playing sniper with the Hunter's Bow on two Fuling Villages in Plains Biome at bottom of Mountain Biome. There was a tiny thin strip of Black Forest separating the two Biomes that allowed me to hide in the trees, unless there was Trolls (Wow, I love this game). Once I started to be able to use Plains Biome resources and began wearing that gear/using that food it got much easier. As you state, I think it is a Progress Wall that the Dev's put in place to slow players down until the next 3 Biomes come out. Honestly, it was incredible fun at that point. Hated the Swamp with all it's jump-scares and darkness.