If the configuration request is taking a long time and not connecting, then it’s likely that there is a firewall which is dropping the openPDC’s packets. Is the openPDC running on the same system as the PMU Connection Tester when you do your testing? If they are running on different systems, then the firewall rules could be different as well.
This could also be an IPv4 vs IPv6 discrepancy. You should try using a pmuconnection file produced by the PMU Connection Tester to configure the openPDC. This will allow you to easily match the openPDC’s configuration with the configuration that was working in the PMU Connection Tester.
Finally, knowing the exact error message coming from the openPDC typically helps to more accurately determine what the problem may be. If you can provide the exact error message you are receiving, I may be able to give you better guidance.