I had the same problem, didn't test it for a while but now I don't see the problem any more. It seems that the bugfix from kernel 4.9.61 has made its way Ubuntu, closing this bug.
Linux tlexps13 4.15.0-22-generic #24~16.04.1-Ubuntu SMP Fri May 18 09:46:31 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
cifs kernel module 2.10
mount.cifs version: 6.4
I had the same problem, didn't test it for a while but now I don't see the problem any more. It seems that the bugfix from kernel 4.9.61 has made its way Ubuntu, closing this bug.
Linux tlexps13 4.15.0-22-generic #24~16.04.1-Ubuntu SMP Fri May 18 09:46:31 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
cifs kernel module 2.10
mount.cifs version: 6.4
https:/ /github. com/torvalds/ linux/commit/ f74bc7c6679200a 4a83156bb89cbf6 c229fe8ec0. patch