New unboxed Cisco ISR4331, command configure terminal didn’t work. Looks like the router is booted in controller mode by default. To get back to “legacy” mode you need to disable controller mode.

Router#conf t
This command is not supported
Router# controller-mode disable
Disabling controller mode will erase the nvram filesystem, remove all configuration files, and reload the box!
Ensure the BOOT variable points to a valid image
Continue? [confirm]
% Warning: Bootstrap config file needed for Day-0 boot is missing
Do you want to abort? (yes/[no]): no
 Mode change success

Wait a few minutes, router will reload.

Router#conf t
Enter configuration commands, one per line.  End with CNTL/Z.

Whenever you update Cisco DNA center, backups stop working. You need to re-apply NFS configuration in DNA center GUI which will restart the docker container and enable backups again.

For example, delete one slash in the Server Path option, write it back and apply. Wait a few minutes for the Docker process to restart. Backups should work now.