Azure backup keeps failing for a month

[de2021]

Can you help me understand why my backup for the past month keeps failing, i have this install on other servers and they all work but on this one server it keeps failing if i select plenty of files. i tested and It worked if the folders is empty or one file.

[#2]

Could it be the files are in use and the Backup service can't scan them?

I would take a look at the Log Files, and/or get a MS support case opened:

Logs are in C:\program files\Microsoft Azure Recovery Services Agent\Temp. In that directory take a look at CBEngineCurr.errlog, which should contain the step by step details on issues.