@Raghuramireddy Vennapusa - Sharing this information for broader community members. Based on one of related support ticket the possible reason found was the schedule associated with the runbook had the resourcegroup parameter missing. By replacing the older schedule with a new schedule which had both the parameters VM name and Resource group Name value resolved the issue.
Please review and confirm the resolution. Hope this information helps broader community members, please circle back if you have any further queries. Thank you