Ok, so here is what it probably isn’t:
- The switch. You’ve swapped it out and both perform the same. The odds of two bad switches in a row is pretty low
- The lights. You’ve added an incandescent. At least it’s not a load issue. If there is some other issue with the wafer lights that’s hard to diagnose.
What it could be:
- The wiring. Probably not but who knows. You say it’s good so moving on.
- The switch’s settings. It feels like a settings issue to some extent. My suspicion, unproven, is that even though the hub says the settings are incorrect, they’re not. It’s as if the MCU is not reacting properly to the remote switches functioning.
I’m referencing a post below where someone had to do settings from both the hub and the switch, albeit w/Aux’s. The only think left I can think of is keep jacking with the settings, both within ST and at the switch. Set them improperly and put back, etc.
Unfortunately, you’re an edge case, which makes it difficult. There probably thousands of installations like yours working perfectly.
As @harjms previously suggested, you could swap for Aux’s.