Unclear Error Message

Receive a mass of the following Messages in Urbackup.log “2020-05-20 14:04:27: WARNING: Small file entry with id 60753730 with filesize=592 hash=nhro4gftvuzmqgi6aP1hkg== has pointed_to!=0 but should be zero. The file entry index may be damaged.”.
No errors in Syslog at filesystem level. Any explanation available which Problem this message adresses ?
Filesystem used is ZFS, dedup and compressed.