As the name suggests orphaned session is like a child that nobody knows whom it belongs to and in session terms, nobody know a specific session whom it belongs to, hence the name orphaned session.
Orphan session examples:
database table lock forever because client and server connection is broken
A user session that the IdP (identity providet) cannot ...
It's difficult to answer your question in detail with the anonymized plan and deadlock, and not a ton of information about what's in the agent job involved in the deadlock. But in general terms, the answer to this question might be useful in helping you track down the problem:
I was at complete loss as to how come an index could cause a deadlock?
Read Committed Snapshot don't affect the lock compatibility matrix.
For reads it means that shared locks aren't acquired, and reads will use row versioning instead. Assuming you are using read committed, that is, since this is the only isolation level that is "reconfigured" by the Read Committed Snapshot database knob.
You evidently have shared ...