Welcome to the Q&A Forum; this is a great place to get support, answers, and tips.
Thank you for posting your question; I'll be more than glad to help you out.
As a SQL DBA (without deep knowledge of Veeam)... what kind of problem do you (or your customer) have?
You didn't post any SQL Server-related error message... what does the SQL error log state during those times when SQL Server should be backed up?
How is the SQL Server configured (regarding storage), there are some known issues with using snapshots and some storage systems/configurations.
How is Veeam configured to back up those servers/nodes/instances?
Snapshots are not the best idea to backup a SQL Server (my personal opinion/experience)
Does that error come from the Veeam backup during the backup of the servers or the Veeam SQL Server backup?
From my "many" questions, you can see there are a lot of options and variables...
Please tell us a little bit more about your problem.
I hope my answer is helpful to you,
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