Dsnodgrass You can check the default storage in the iPad settings in the PureFlow section (see screenshot below). By default it should be iCloud or On My iPad if iCloud is not available.
I guess you created the document while the Recents section was selected. Am I right?
By default PureFlow saves to the PureFlow folder (in iCloud or on iPad). You can check if this folder is empty in the Files App. Or you can navigate to this folder in the PureFlow app, on the first screen. I guess you can also check Recently Deleted folder, or the Recents section in the Files app, or use search in the Files app. But actually I doubt the file will be there.
If you can't find the file, I guess you work is lost. I'm sorry fir that.
I will try to reproduce and fix this problem, but I've never seen such an error before. It needs further investigation.
Also, could you please create another document and check if the file was created and the diagram was saved? Try saving in different locations.
Also did you use export or share functionality? Linke OzLand said above.
Dsnodgrass There is no save function icon that I could see.
Yes, it autosaves the document every 30 seconds.