I don’t know why they disappeared but it is curious and shouldn’t happen.
Luckily everything created through PaperUI gets stored in /var/lib/openhab2/jsondb/backup.
Look in there. The big number at the front of the file names are the timestamp so pick the set of files with the biggest numbers and copy them back to /var/lib/openhab2/jsondb, removing the big number from the name.
Do all this copying while OH is stopped.
If you are unlucky, whatever wiped out your original jsondb files also wiped out your automated backups.