Fusion page ok, but Edit/Color Media offline, beta6

I re-opened a project built in beta5. Two clips (h264 high L4.1) of about 2 minutes in length (using most of the source clip) are now showing as Media Offline in the timeline Edit and Color pages... but in the Fusion page the video appears fine (and they are fine in the source viewer).

The fusion composition is a simple paint node applied between mediaIn and mediaOut. I rendered this yesterday without issue in beta5.

In the edit page, I can play and hear the audio, but no video visible.

"Relink selected clip" on each of the source videos in the media pool caused the video to reappear (at least within the current session).

Some other items that might help in diagnosis:
* I had deleted the cache after the rendering yesterday (and before the upgrade to beta6).
* Only two of the similar three clip sections that had the paint applied were showing up as "Media Offline", which was quite puzzling.