Multiple termination transactions failed

We have a following rule configured for Termination transaction:

There are no specific transactions and only notifications are configured. The transaction were working fine multiple months but starting from this September most of them are failed (but not all). After recover action some transactions were successfully completed (but not of them).

Issue description is the following: "Error caused by SOA component or the underlying HWF configuration or a Supervisor hierarchy setup issue".

We've checked multiple times that employees with failed transaction have all needed approvers (Managers, HR Representative and etc).

Could you advice please what can be the issue?

Thank you!