Seems like there is something fundamental that is wrong. 2 RIOs and PDP and PCM are misbehaving? Maybe there is something going on with the actual wires.
Try this, grab two clean/prestine new wires, cleanly strip them, insert into the RIO and PDP's weidumuller connector. Be sure to press down on the white button before inserting the wire. Tug-test them by pulling on the insulation and make sure the wire doesn't pull out (doesn't require too much effort)
Video on inserting wire:
https://youtu.be/kCcDw3lDYis
Source from:
https://wpilib.screenstepslive.com/s...control-system
Maybe a photo of the wiring between RIO and PDP will reveal something obvious?