Server's error: Fatal error during backup. Backup not completed

Hi All,

Urbackup server 2.3.7 on Asustor 1002t, client 2.1.17 (Centos 6), error during incremental backup. Full backup log sent to bugreports@urbackup.org.

18.09.19 11:57 ERROR Fatal error during backup. Backup not completed
18.09.19 11:57 INFO Transferred 35.7837 MB - Average speed: 246.064 KBit/s
18.09.19 11:57 INFO (Before compression: 138.514 MB ratio: 3.87089)
18.09.19 11:57 INFO 102.237 MB of files were already present on the server and did not need to be transferred
18.09.19 11:57 DEBUG Script does not exist urbackup/post_incr_filebackup
18.09.19 11:57 INFO Time taken for backing up client webhosting1: 21m 28s
18.09.19 11:57 ERROR Backup failed