I finally give up on AOMEI BackUpper Server
After using this software for a year or two, I finally went back to Windows Server Backup. This software is nice and very inexpensive, but it also is very unreliable.
I kept getting "memory too low" error at least twice a week. I had about 25GB of Ram available when I got those errors.
The suggestion is to reboot, create multiple backups etc. This is not a solution. A backup software for a server needs to be able to handle 1.2TB of data without blinking.
I still have a second copy running on the webserver, and I will keep that one, since the data is very small.