One thing I also did is in my HomeGenie setup I disabled all the x10 programs I had that essentially repeated a PLM command for a device as an RF command (I had originally had issues with some x10 commands not reaching things on the opposite phase, and this approach worked).
There is nothing specific connected from the P2 to the PiX10Hub other than they both send / receive X10 commands.
I think this action may well have resolved your issue. Definitely sounds like X10 signal duplication/collision. Not sure what you have installed on that PiX10 hub as there's a number of different "versions" circulating, some with HA Bridge, some without and others with various other items installed.
A straightforward install of HomeGenie should happily coexist with your setup. You've basically two X10 controllers operating on your setup, the CM15 on your Raspberry Pi and your Harmony hub and it appears they are duplicating the same tasks each time you issue an X10 command. Bearing in mind that the Harmony hub allows your setup to interface with Alexa that should be your main focus. I'd be surprised if you're not getting lockups on your CM15 too but they are not as obvious as the ones on the Harmony hub.
What ports are currently in use on your network. Have you checked what port Harmony hub uses. Have you HA Bridge installed. Is that conflicting with either the Harmony port or the HomeGenie port. Can you see the possible conflicts in your system. I've no doubt that your Harmony hub is fine, it's just all the other elements on your setup I couldn't be sure of. You've definitely got conflicts here. It's just knowing how your system is configured would help eliminate the conflict.
As you say let it run with the changes you made and report back. Do bear in mind @brobin uses the Harmony hub but not the PiX10 hub. I use HomeGenie but not the Harmony hub