I'm a bit lost on what else to troubleshoot for my issue, here is what is happening on my 2017 Suburban LT:
• Front Air Conditioning (cooling or heat) work normal and blow at speeds set by the HVAC controls
• Rear Air Conditioning does not blow anything (cooling or heat) from either the front control panel for the rear vents or the rear control panel located on the back of the center console

To be clear, this is not anything with blowing cold air or heat, there is no air at all coming from the rear vents as the rear blower doesn't turn on at all.

Here is what I've tested so far:
• Rear blower motor fuse is working
• Rear blower fan will spin up just fine if I directly hot wire it to a battery (bypassing all the normal wiring/fuses/etc.)
• Rear blower fan harness (goes from the resistor to the blower fan) is working - I also directly hot wired a battery though here and the blower fan spun right up
• Rear blower motor resistor has power both coming in and out (to the blower fan) when I have the rear air set to on
• Rear blower motor resistor has been replaced with a known good working one twice
• I disconnected the rear air control panel (on the back of the center console) and the front rear air control panel functions but no air is coming out still (I wasn't sure if there was a control unit built into this panel)
• The rear air control panel (on the back of the center console) controls seems to be functioning - when I move the fan speeds or air position, it reflects immediately on the front rear control panel screen

I just have a basic reader but did see a DTC for the following:
U15FO Status: HISTORY - Lost
Communication with Device on LIN Bus

I don't know if the DTC is related or not as I did not pull this until after I started all the troubleshooting above so it could have shown from all the stuff I was doing.

Does anyone have any other things I can check for this issue?