Same Issue. And with only 1 export allowed on demo version this is a terrible first impression. I like the program but my end result after hours of editing leaves a bad taste in my mouth and leaves me hesitant to purchase.
Using v 13.51
[UPDATE]
I suspect it has to do with "Building the preview" message that can occur while previewing the sequence. I managed to avoid it at one place in particular by removing the "blur" effect between clips. I hope this helps!