Note that restic has known unresolved problems with backing up to cifs shares due to some underlying go implementation details deep down in the stack:

restic fails on repo mounted via CIFS/samba on Linux using go 1.14 build https://github.com/restic/restic/issues/2659

Of course there are some cifs issues in the borg tracker, too, but most of them seem to be based on unreliable network connections - while the restic problem seems to be related to golang details.

With backups I would rather not trust a tool that has basic problems like accessing files on a network drive, but this is just me.