We have seen this issue reported recently.
Path \nas-name\file-name does not exist!
The file path shown in the error was never explicitly selected in the source selection within the backup job.
Also, there are two spaces before the last "
Both of these are atypical of how the system works.
We upgraded to version 18.104.22.168 and that resolved both issues
AhsayOBM, NAS backup, v7