Backup can not be created in Plesk with one of the errors below:
Document is empty, line 1, column 1 (, line 1)
None (line 0)
- #PPPM-13765 "Creating a backup of the Plesk server no longer fails under specific conditions."
This issue is planned to be fixed in upcoming release 18.0.51. Until the fix is released, there is no workaround.