In your project settings, where you create create your folder path for captured video/audio, project auto saves…you can also save the path for video/ audio previews. I found that (and I have no real explanation why i tried it or why it worked) that when I have a folder on my system drive (in my case, the desktop) and save preview files there, instead of the folder/drive where the source footage resides, that things became more stable.
Do you see a little yellow “caution” triangle or red “stop sign” on the very bottom of your screen? sometimes thats an unnoticeable indicator of errors.
-jason
-jason