I ended up walking around aimlessly for a little bit. I didn't find the cauldron at first, and so didn't know what to do with the ingredients. The player ends up spawning just slightly above the viewing range of the cauldron, so I didn't even know it was there until I looped back around and stumbled across it. By that point, I had a full inventory with ingredients, and attempting to open the cauldron causes the game to crash. Upon restarting, I immediately went and found the cauldron, which now let me open it. So the bug appears to be if you have ingredients before opening the cauldron for the first time.
As for the cauldron itself, the crafting mechanic is neat at first, but having to guess the recipe for these potions is... not good. I am not going to sit here and go through every combination of ingredients before I find each potion. I only discovered the recipe for the swiftwind tonic. After crafting one and using it, the speed boost only lasted a few seconds, which I suppose is fair.
Ultimately, the game works; without these issues, I feel that you have a good foundation for a horde/wave style game. Hopefully you carry forward what you learned for the next game! Good luck.
EDIT: I really dislike games that start in full screen. I know it's a harmless thing, and you have a setting to disable full screen, but it still irked me upon opening the game. It's just one of those personal issues, but it really does take me out of the game's ambiance almost immediately.