Corrupt file?

Stager v3.0.3 On Mac M2 Sonoma 14.6

I saved my file yesterday and it was fine, but when I came to open it again the preview was corrupted. Also all the folders in the stage area had disappeared and nothing can be done to move objects around or access the menus or select objects. Rendering is disabled as well. When I open this file I am unable to quit it and have to force quit.

It looks like the below screenshot whereas it should be a full colour image of a display unit. I've not had this problem before in either Stager or Dimensions. Like I say it looked fine when I saved it. The same is true of the autosaves. Any ideas what's going on here?