where are you sending the local backups? Is it to a local disk or to a network share?

It is to a usb attached drive.

how is the USB drive exposed by the OS? Drive letter, mapped drive? Same drive attached to one server but accessed by both or do you move the drive?

They each have their own USB drive. It is never moved, and it does have a drive letter assigned.

When you plug in a removable disk, Windows assigns it the next available drive letter. Depending on what devices you plug in and remove over time, these automatically assigned drive letters can change. I do not know if this is the issue, but if you set the backup plan to back up to the D: drive because that's how the drive is normally exposed, and Windows assigns E: the next time the drive is plugged in, the local backup will fail. Can you verify the drive letter assigned in Windows matches what you are using in the backup plans? Also, you can assign a permanent drive letter using this method: https://www.groovypost.com/howto/assign-permanent-letter-removable-usb-drive-windows/

Thank you David for your quick responses. There are no issues with the drive assignment. I have verified it. What is strange is that it appears to be working despite the error. I check the backup storage tab and drill down to the individual backups; they appear all there. As I said, I am restoring to see if it is ok, but I don't expect any issues. By the way, this was fine before those aforementioned versions where installed; so years (yes years) of no issues with respect to this. Also, it is very strange that both sites (completely independent of each other) exhibited this same behavior right after the update.

Hello David, As nobody can seem to help me with this issue, can you provide a link to the version before 6.3.2.204 please.

I have the same issue

Please open a support ticket using the Tools - Diagnostic toolbar option and reference this post. Support can assist with older versions as well.