The "Backup Main LS Host" and the "Backup Main LS Port" fields in the Location Server configuration must be empty in all SpectroSERVER configurations. The Location Server code keeps track of the SpectroSERVERs and by the precedence values knows which SpectroSERVER is the backup. Clear these settings. Once the changes are saved, the Location Server needs to be restarted.
Then you may need to reload the SSdb database on the secondary MLS host.
../SS-Tools/SSdbload -il -add precedence savefile