Hello! I recently downloaded the 7.50 free version, and I am having the same issue (the project plays perfectly when watched in the preview and is completely out of sync after it's exported).
This is the link to my project:
https://drive.google.com/open?id=1CJKjyLZHqQn_Q9BZ9pk8Rlc6eRSYfMTT
I would appreciate if you could or the developers could help me analyze it.
Thanks.