Comment 4 for bug 1572132

This seems like a sort of known issue (unclear still). Cursory grepping in fs/cifs:

readdir.c::find_cifs_entry

        /*
         * If first entry in buf is zero then is first buffer
         * in search response data which means it is likely . and ..
         * will be in this buffer, although some servers do not return
         * . and .. for the root of a drive and for those we need
         * to start two entries earlier.
         */

It might be helpful to enable some more cifs debugging by booting with

dyndbg="file fs/cifs/readdir.c +p"

appended to the kernel commandline?

Also, is there a reason you are passing 'nounix' specifically? It seems like an uncommon option to need.