Disappearing Canvas

I made an OmniGraffle document that had 2 canvasses in it a couple of days ago. When I re-opened it, one of the canvasses was missing. I looked in the Dropbox to try retrieving an older version and every one contained a Finder Quick Look preview with 2 pages, but when opened, only showed 1 canvas. This is perplexing. That canvas was about an hour of work.

weird, sorry. did you send the file to omni for troubleshooting?