Sorting by organisation on the users page is a bit broken because of the way the join is done so don't offer the capability to do it in the first place...

src/Sprunje/UserSprunje.php

@@ -31,7 +31,6 @@ class UserSprunje extends UFUserSprunje
     ];
     protected $sortable = [
         'name',
-        'organisations',
         'last_activity',
         'status',
     ];