Set your docker custom network to 'ipvlan' instead of 'macvlan'.
You have network or remote server issues. The mount command is taking too long:
Dec 13 18:03:13 Unraid-NUC8BEH unassigned.devices: Warning: shell_exec(/sbin/mount -t 'cifs' -o rw,noserverino,nounix,iocharset=utf8,file_mode=0777,dir_mode=0777,uid=99,gid=100,credentials='/tmp/unassigned.devices/credentials_scratch-DS411' '//DS411-II/scratch-DS411' '/mnt/remotes/DS411-II_scratch-DS411' 2>&1) took longer than 10s!
Dec 13 18:03:13 Unraid-NUC8BEH unassigned.devices: SMB default protocol mount failed: 'command timed out'.
Try using the IP address for the remote server instead of the name and see if it makes a difference.