GE 3-Way Kit (45609 & 45610) - Tips for troubleshooting Aux?

I’ve spent about a week looking at this and I am running out of ideas. I have a 2 gang box at the bottom of a stairwell and 2 sets of the GE 3 way kit. One set handles the stairs and the other handles the foyer light. The 2 gang box hosts the 2 primary switches. Those look to be working fine with the blue led and switches work as expected for both. My stairwell aux works fine. The foyer aux doesn’t.

[ul][li]Swapped out the Aux with the known working one from stairwell. Foyer Aux still doesn’t work [/li]
[li]I measured the voltage coming out of the traveler wire on the primary foyer switch and it said 118. When i tested the voltage coming out of the traveler of the stairwell primary switch, it said ~122v.[/li]
[li]I measured the voltage on the traveler on the aux that wasn’t working and it said 118 also. The stairwell aux traveler was showing ~122.[/li][/ul]

Do you guys have any other ideas for combinations for me to check with a multimeter? Do we know exactly how much the voltage should change on the traveller when the switch is pressed?

I see two possibilities remaining.

The foyer traveler wiring may be bad or the main switch may have a problem.

Since they are conveniently located in the same gang box, I would try swapping the known good stairwell remote and traveler to the foyer main switch.

If the stairwell remote can then operate the foyer main, then the foyer traveler wiring is at fault.
If the stairwell remote cannot operate the foyer main switch, then the main foyer switch is at fault.