In the iOS app, I have an error for 1 Unsynced time entry. If I try to delete the entry, it comes right back. It doesn’t appear in the web app.
Did you originally create that time entry, or was it created via an integration, perhaps?
If this is the only time entry with syncing issues and you are sure there are no other entries with an error icon next to them in the form of 
or 
please log out and log back in - this should get rid of it. Let me know if it helps.