The priority sorter plugin is currently built againt Jenkins 1.580. But also againt folders plugin version 5.0
Folders plugin 5.0 has as minimum version 1.609.1 of jenkins.
I have a jenkins on 1.580.3 and folders plugin 4.10
If I enable in a jobgroup "Jobs and Folders marked for inclusion", I get the following exception when configuring a job
Caused by: java.lang.NoClassDefFoundError: com/cloudbees/hudson/plugins/folder/AbstractFolder
So either the plugin is fixed so it can handle also older version of the folders plugin, or the minimum required version of Jenkins is set to 1.609.1