The functionality for the UI action "reapply assignment rules" does no longer work after the plugin upgrade.
Paris Patch 2
Just to reiterate Apply Changes button on the Assignment Rules list page will rerun all the changed rules on all active Open Vulnerability Items, except those that were manually assigned.
There is a field on the VI called 'Assignment Type'. If the value is set as Rule, then Assignment Rules will apply to the vulnerability item. If the 'Assignment Type' is manual, then the Assignment Rules condition will not trigger on those Vulnerability Item Records.