Hello DRCallah being a retired IBM engineer means I probably used one of your systems as a kid.Please said with all due respect of course.
I am a little intimidated in giving you PC advice being from IBM and all but even us engineers and technologists sometimes overlook the simplest solutions.
(I'm missing a few courses to complete engineering degree,got good job years ago so put it off many many years)
You began by saying upgrade from CM11 to CM15?
By your tests we can assume it is X-10 related problem.Either new soft install or install bringing up old hidden cm11 related soft/drivers?
Have you tried un-installing all X-10 software and drivers but leaving CM15A plugged in on shutdown?
Is it possible that somehow there is an old CM11 related driver or code that was not removed?
When you're PC time resets is your BIOS settings affected as well?
I am convinced it is X-10 but whether AHP (since clock is fine if USB unplugged) is responsible is 50-50?
If and I am sure you have done this already,cleaned out all CM11 drivers and software then the problem lies between your USB and CM15A itself.
Possibly have a Defective USB cable or CM15A or maybe (X-10 makes this a valid question) both are defective.
I'm pushing for a defective CM15A more than the cable.Try a cable known to work on your PC (same type if possible).
All i can say is try uninstalling AHP drivers and software.Run something like ccleaner for issues and then re-install.
If it still does it ask for RMA or if you do not wish to go through above remove-install than request RMA.
Hope you resolve your issues quickly without to much aggravation(if that is at all possible with X-10).
Good Luck and please if you do find the problem let us know.It would be helpful to others I am sure.