Thanks to a random youtube video, I saw that all events in Stage 5 were broken!
Not a single one worked, not even the elevators.
Long story short, I was able to fix it after a whole afternoon of debugging and going through all the scripting. Turned out it was one tiny but of code that didnt have the right reference - and that was enough to destroy the whole level.
Gladly I was able to find the Issue and fix it.
You can enjoy STAGE 5 as intended again.