Task actions are not tested with workflow.
Most (if not all) of them must have injected a component which is no longer provided in current M6.

via MGNLUI-4792:

info.magnolia.ui.admincentral.shellapp.pulse.task.DefaultTaskDetailPresenter is now bound to admincentral M5, so the component mapping is indeed not there in M6; we'd have to adjust the action(s) :#

• we might consider a "compatibility bridge" there too with a fake impl; cuz those actions might be used in workflow and elsewhere
• said presenter is extended in workflow (hint hint, more to check)
• all AbstractTaskAction would previously inject it, since it was in its constructor until last month