Having upgraded, done fresh installs, of Ubuntu 17.04 I noticed that the SAMBA/cifs client didn't behave as expected. When mounting a volume shared from OS X (Sierra) it would work for a while before the client started DDOS'ing the server to such an extent that no other users could log in.
We then tried to connect to a windows share (windows server edition), but with a basic fstab entry it would throw an error:
mount error(5): Input/output error
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
Apparently the cifs protocol defaults to using v1.0 of the protocol. By adding "vers=2.1" or "vers=3.0" to the mount options it will mount correctly.