Diarium version: 2.8.16
OS + version: iOS 15.2.1
As I mentioned here, on plane WiFi on iOS, the "uploading local database" window would stay up for a long time (I took a screen recording of it lasting at least 63 seconds). Sometimes, when I would go to another app and then come back, it would say that it failed, but then would attempt syncing again immediately after I started trying to edit an entry. (Sometimes it did not do that, and I have no idea why). Since you can't use the app when that window is up, it made the app fairly unusable.
What I think would be a simple fix for this would be to add a dismiss button to the syncing window (or just allowing you to tap somewhere outside the window to dismiss it) so that you can still use the app while it's trying to sync (or, if that's not possible, to make it stop trying).