mobs usually dont stick around especially if you died at night, night spawned enemies despawn.

Your mistake was venturing to the mountains at this point, you should've gone around. Mountains is considered "biome 4" intended to be visited after the Swamp.

The game has a lot of jank it is true and i myself complain a bout it a lot but you also need to understand the idea of how things are tiered and intended to be taken on. I dunno if you just stuck with leather armor or what but I recommend using troll leather armor, its faster to make than bronze which is not at all worth it for the amount of materials needed to make it, and is immediately obsoleted by iron armor. You should get a finewood bow to do a good amount of your work at this point. If you're really struggling, make the bronze atgier and use the alt (middle click) attack, this will stun enemies.