Could you also send me your project file itself? (the .tpy file)
Is it possible that this happens for photos which are missing? I.e., either because you removed or moved the photo after importing them into Tropy? In the screenshot above, there are a bunch of photos missing (marked with the exclamation mark icon). One of the recent updates changed the way Tropy generates thumbnails, so all photos will be consolidated after the update; it is my guess that this is the reason why the error started appearing after the update.