Product version?

Do you know if those servers have the updates from Microsoft installed. I see some reference to this error on the internets that talk about a fix in the July 2020 Windows Server update.

You didn’t mention the types of backups you are running, but if file backup using legacy format, do you happen to have any folders being backed up with 100’s of thousands of files in them? Not saying that’s the issue. I have not been able to find a reference to that error in our system, but I’ll wait for your reply before reaching out to support.

Both just File Backups, 7.2.1.58.

Will check and confirm the updates and fs for any issues and revert.

Both servers are fully updated, number of files isn't above average for file backups.

at this point you can either reach out to support via the tools diagnostic toolbar option, which will send the logs to them for review. The logs may contain some additional information that is not visible without a closer look.

Or you could try upgrading one of the servers to a more recent version of the software to see if that addresses the issue.