Note: This issue was resolved in the newer NovaBACKUP 21.2.422 client version (released on April 22, 2025). It is advised to upgrade to that client version.
As stated in the NovaBACKUP version changelog for the 21.2.404 client version here, in the "Known Issues or limitations with this version" section of the changelog for that version, for the first item in the list, that is regarding a problem that we have identified in the 21.2.404 client version. This problem only affects specific Windows Server OS's that are running the latest 21.2.404 client public release version, and we know that it was not a problem before in 21.1219.1 which was the one prior release version to that, so it is a regression.
Windows Server 2019, Server 2016, and Server 2012 R2 OS's may not be able to backup to Local Backup devices that utilize a network path that is a protected (secured) Linux based network share. In that case the backup jobs, that were working well to that same device in versions prior to 21.2.404, may stop working after upgrading to the 21.2.404 client version, and usually the backup fails quick with the error "Unable to connect to network location: \\192.168.1.2\NAS\. Error: The network path was not found.". The only known workaround for this for now, until we know more, or a fix is provided for it, is you must downgrade the client version to the one prior 21.1.1219 client version, which we aren't seeing any reports of problems with that client version for this OS specific backup problem. You can follow the KB article here on how to perform a client downgrade for that. Note: Windows Server 2022 OS does not seem to have this backup problem, nor does Windows 11 and Windows 10.
If you are running a Windows Server OS that is less than Windows Server 2022, if you do notice that after either upgrading to or clean installing the 21.2.404 client version, that the backup to a 'Local Backup' device that utilizes a Linux based network share as the path value in the device, fails quick with the error "Unable to connect to network location: \\192.168.1.2\NAS\. Error: The network path was not found.", especially if that device was working fine prior in an earlier client version, then must downgrade the current installed 21.2.404 client version to the one older 21.1.1219 client version, by first uninstalling the current 21.2.404 version and when prompted to remove the application data during the uninstall, uncheck that box to keep the application data, and then once uninstalled you can install 21.1.1219 (download here: https://filestore.novabackup.com/Downloads/NovaBACKUP/21.1/Setup-NB-Server-Agent-21.1.1219.exe). Once the 21.1.1219. backup client is installed and is running you likely will need to go to the client "Default Settings > CMon Server" tab dialog, and re-enter your CMon Server details as prior, as those files may in fact be null/blank/not configured anymore, if CMon communication is needed. You may also want to disable the "Update client version on next job run" option in the client "Default Settings > Notification" tab dialog; doing that step will make if so that the next job run won't automatically upgrade the backup client version to either "21.2.404", which is the current client public release verison, or any newer client version going forward (which is only enabled for certain customers, and client licenses, and only if the CMon Agent part of the client is in the connected state I believe, which you don't want the client to auto upgrade the backup client version in this case, because then the same problem will repeate on the subsequent job run after this one that does work, at least until we investigate and fix this problem. Then after that, start the 21.1.1219 backup client and then open and run that same existing 'Local Backup' network path based device assigned backup job via the "Backup" tab or the "Schedule" tab, and run the backup job there and see if it runs and can make it at least to the "Snapping" and then the "Scanning" states that come in that order, otherwise it would have failed prior to that point in 21.2.404 if you did have this issue, and is able to complete fine on the older 21.1.1219 client version in that case (if it has the same problem or will fail the backup job within about 1 minute we have seen so far in early testing on at least the Windows Server 2019 and 2016 OS's, at least for Linux based network shares that the 'Local Backup' device is assigned to). And if that fixes your stated problem on one Server 2019 down to Server 2012 R2 machine, then you'd likely want or need to repeat these same exact instructions on any of your other less than Server 2022 OS machine(s) that will likely hit this same problem if they do backup to either the same or a similar 'Local Backup' device, that also uses a Linux based network share as the "Folder or Network path" specified value in that device (in the Device tab) that is assigned to backup job(s). This KB article and the changelog will be modified when we know more about this problem, that only exists in the 21.2.404 client.
Note: This issue was resolved in the newer NovaBACKUP 21.2.422 client version (released on April 22, 2025). It is advised to upgrade to that client version.