Leave request WS21500001 not visible to manager

Hello WF Experts,

We are using standard SAP Workflow WS21500001 for leave requests. Its not modified.

Employee registers his leave, workflow is started and goes to task TS21500003. In this moment work items should be visible in manager's inbox for approval. And it is in 99%, but sometimes managers doesn't get any work items. In SWIA I can see, that they are in status READY. When opening Workflow log and checking for agent I am getting message 'No selected agents'. No errors in step history.

In PTARQ I can see different picture. Status for leave is SENT and correct manager found in fields 'Next Agent' and 'Pers. No'.

I've also checked OM and it hasn't changed at that moment. Org.unit was in the same condition.

Any ideas?

Possible solutions for existing issues?

I've tried to find a way how I can forward leaves to new/same manager, but it looks like SAP doesn't have standard program/solution for that. In ptarq we can only post, approve or delete leaves.