Never Ending OLEDB Wait for Linked Server
For SQL Server targets:
On the target server (the one that's receiving the linked server query), run sp_WhoIsActive and look at the linked server query.

If the query doesn't show up, something's going awry with the linked server query and it's never reaching its destination.

If it does show up, look at the Wait column, and see what the wait type is. (It won't be OLEDB.) That'll help you troubleshoot the reason it's not completing. Feel free to post that in with your question, and I can elaborate more on that specific wait type.

For non-SQL Server targets like the IBM/Rocket one in this case: you'll want to work with the sysadmin/DBA on that platform, and have them check the progress of the query. When you see OLEDB on the SQL Server sending side, you just can't tell anything about what the holdup is on the other end.