Problem
The variable %LOGONSERVER% is not evaluated at computer startup - therefore it is not usable within logon GPO’s to build up a simple rollback-configuration if one dc is not reachable.
Solution:
In Samba 4 environments each domaincontroller registers itself in the forwardzone. With the help of that you can simply use the domainname as a refferal for the sysvol/logon script location and as an alternative for finding a suitable domaincontroller:
\\domain.test\sysvol\logon