Crash should be fixed in new version. If you want to test harvesting the demolisher boulders you also need to turn off the "auto-build in sandboxes" option for Blueprint Sandboxes.
(Crash was happening because the boulders get marked for deconstruction for all forces, but as soon as the blueprint sandbox force marks it for deconstruction it gets deleted instantly and then the other forces try to mark boulders for deconstruction but they no longer exist)
