Hello AK,
After you reassigned an active resource, did you click on "Retry"? If even after retry the process doesn't move, you may be hitting on a known Clarity issue.
CLRT-75811 - If a process fails with message "BPM-0532: There are no assignees to send the action item to." process will not move any further after reassigning the action item and retrying the step. This issue is currently under review by CA Development Team.
Thanks and Best Regards,
Ruchika Israni
Sr. Support Engineer
CA Clarity