Recently I encountered an issue with our Ubuntu clients mounting samba shares who authenticate via ldap. Our clients are configured to automatically update throughout the nights, upon reading I discovered that some updates may have caused the problem which I yet have to discover. Fortunately, a quick edit on our pam_mount.conf.xml did the trick.
The following lines contain "vers=1.0", please note that depending on your server/client the version may differ. Also previous configurations had worked perfectly fine for years without explicitly stating the version.
Hope that helps!