The problem is the auto-backup, the backup no longer saves the tabs (this empty). Therefore, when the add-on is update and loads the last backup there are no more tabs.
I've had to disable auto-backup and restore my tabs manually with my last correct backup (2019-08-26).
Hi! Your problem is closely related to this Firefox bug (I am created): https://bugzilla.mozilla.org/show_bug.cgi?id=1580879 We need to wait until the developers of Firefox fix it...
