Transitions/Overlappings = Crash ??

I made a movie consisting of several video clips.
I overlapped some clips to create transitions then.
First time everything worked fine, I could play the video and see the transitions.
Next day I started Shotcut to export my video, the export failed at 40%.
I tryed several times to export, but it constantly stops at 40%.
Also everytime I play the video now, shotcut crashes when a transition appears.
I tryed to remove the transitions and everything worked just fine.

So I guess the bug has to do something with the transitions.

Is there any way to fix that problem? I know that I could remove all transitions but the movie wouldn’t be synchron with the music then (Due its a music video)