I have discovered , and others have confirmed, that if you sync a photo that has been edited in PS and saved as a PSD the syncing status will say the photos are not synced. See photo below. In fact they are synced but they remain in the un-synced status forever. When you exit the program you get an error that there are un-synced photos. Other photos edited in LR are not affected. I believe the problem only occurs when you edit the photo a second time after it has been previously added to a synced collection. The majority of my work flow involves editing raw in Lightroom Classic and then round-tripping to Photoshop resulting in a psd returned to Lightroom Classic. I frequently put the edited photos into a synced collection. If I re-edit the psd, the file appears to sync across platforms but Classic reports an endless sync in progress. When I remove the file from the collection, the sync status turns green almost immediately. When i put the edited file back into the collection it immediately syncs! I did find that Photoshop editing was the issue and the problem also occurs if round-tripped in tiff, not just psd. It also didn't matter if the file was complex or very large (note that psb large format files do not sync--that is a known limitation). All programs are up to date. I am using Windows 10 64 bit also up to date.