[Samba] Certain systems can no longer access samba post upgrade to 4.3.9

[Jeff Hodge]

During an ubuntu 14.04 update samba was updated from 4.1.6 to 4.3.9.  We
had no problems with any windows system accessing the server prior to the
upgrade to 4.3.9.  It seems to affect access to the entire samba server as
no shares are able to be seen or accessed when trying to view \\servername
or \\servname.domain.local

The "fix" seems to be to use the fully qualified name, but after a while
that will stop working and you have to change to the short name and vice
versa.  I am trying to correlate the times to see if there is a pattern,
but no pattern has emerged yet.

What is odd is if the short name is failing and you change to fully
qualified and the share comes up, you will then be able to use the short
name to pull up the share after you have made the successful connection to
the fully qualified name.

The one log entry that seems to identify systems with this issue is this,
repeated over and over:

[2016/08/29 08:35:56.694436,  0]
../source3/param/loadparm.c:1460(canonicalize_servicename)
  canonicalize_servicename: NULL source name!

[2016/08/29 08:35:57.694984,  0]
../source3/param/loadparm.c:1460(canonicalize_servicename)
  canonicalize_servicename: NULL source name!

[2016/08/29 08:35:58.694495,  0]
../source3/param/loadparm.c:1460(canonicalize_servicename)
  canonicalize_servicename: NULL source name!

The majority of our servers are not having any problems accessing the samba
shares, but a few key high use systems are having this issue.

Has anyone seen this error and may have an idea what may be causing and
possible system setting that may need to be changed/enabled in 4.3.9 to
allow all systems to connect reliably?