Thanks for the clarification of the behavior. As you expected this is NOT what POM should be doing. We have not directly seen this with any of our customers, but a quick search of the Avaya support notes turned up the following that sounds similar:
POM Agent Receives 2 Nailup Calls
Doc ID: SOLN352095;
Published date: 12 Jun 2020;
Updated: 12 Jun 2020
Author: Donna Briggs
AEP 7.2.x POM #.x
Issue with POM placing a second call to an agent
New installation in lab, initial testing of the POM OOTB campaign with the Syntelate desktop
Second nailup call to agent within seconds of first nailup call
If you have support with Avaya, I'd suggest opening a ticket and getting Avaya support involved. If you find and read the rest of this support note, you'd find that the problem had to do with a missing EP root certificate:
There was no EP root certificate present in the application trusted store. According to POM documentation, the EP root certificate must be imported into the application server trusted store, which is then the CA certificate for both EPM and MPP. In this case, both MPP and EPM certificates are signed by customer CA. The application server cannot trust the MPP because neither the EP root certificate or the customer CA is present in its trusted store, only the EPM server certicate is there.
I'm not certain that your issue is identical since the duplicated call is coming from Nailer when the only call to the contact should come from PomDriver. That said, there may be another support note that is directly your issue. Regardless, I think a ticket should be opened with Avaya to figure out the cause and fix it.