Error sync after deleting cards on either iPhone or desktop

After I edit cards on either the desktop anki or on my iPhone and sync, I always receive an error on the other devices when I tried to sync. The error would say “please use the check database function, then sync again. If problems persist, please force a full sync in the preferences screen.”

I have tried the check database function on both devices (the device that deleted a card and the device I’m trying to sync changes to), but they do not resolve the sync issues. Force one directional sync does work, but it usually takes a long time and I might also lose progress.

Please let me know if any other information would be helpful. I would appreciate any advice and thank you!

After using “check database”, please sync and choose “upload” to send the changes to AnkiWeb, and then sync any other devices, choosing “download”. That should bring things back into sync: Syncing with AnkiWeb - Anki Manual

Do you know if there’s a reason why I keep seeing the “please use the check database” function? Is this because of an add-on? Thank you!

It’s possible. If you disable all your add-ons and repeat the steps above, does the issue still occur? You also don’t appear to be using the latest Anki version, so I’d recommend updating to the latest before you test.