Specify SMB 3.0 in /etc/fstab
Solution 1:
I had the same problem which was also due to an upgrade to one of my institute’s servers. I managed to mount the share by adding the vers=3.0 option to fstab without the -o argument.
sudo mount -t cifs //192.168.1.100/Movies /mnt/Media vers=3.0,user=plex,uid=111,gid=1000,pass=PASSWORD