Hi, I seem to be having this same problem too. I'm a new user just evaluating the software and already running into issues.
The first day everything seemed to be fine. Not sure what I did but then suddenly everything got out of sync the next day. I have a clip that I split and add different portions to my sequence. The audio plays the correct portion but the video shows a completely different portion.
I tried recreating a completely new project from scratch, still using the same source files and just tried cutting 2 clips to add and right away started having the same problem. I've tried the clear unused cache, but the issue is I want to clear the current in use cache.
This sounds like a pretty bad bug that needs to be fixed. Hard to believe you can't do something so basic in an editing program.
As the OP suggested, is there a way to force it to re-render the preview?