Hello GersDev,
thank you very much for playing our game. Are you using an Intel GPU? I realized, that you are missing some textures. There should be no invisible walls in this game and I apologize, that you encountered that issue. Upon further investigation, there is a bug in the Godot engine, where textures disappear, when there are to many present at the same time. I uploaded a fixed version (gles2_windows.zip), that hopefully will resolve your issue.
For anyone using the Godot engine: I would recommend to compile the game by using GLES2 AND GLES3. I tested this today on two different Intel GPU computers and this bug was resolved on both of them.