This sounds like your game is damaged somehow. You could try to create a new test game, place two levels in it and one door for each level. Than all you have to do is to connect the doors with each other and try it out. If the doors are working in your test game, my guess would be there indeed is something in your game, which is damaged.
I’ll create a test game myself too. The engine has been updated recently and this might have something to do with it. I’m curious if it’s your game or the whole engine. In any case deWiTTERS is the only one, who can help. However, to discuss the issue here probably will help him to save time in order to find the issue.