Ultimately, I was hoping to achieve scene control with smart bulbs on a three way circuit.
Originally, I had the Red switch and a dumb switch working perfectly together just like a 3 way circuit should work normally.
Remove the three way from the discussion for now. I have a Red series switch connected to ceiling pots containing RGB bulbs. With local control enabled, I switch the circuit ON and OFF. If I disable local control then I have more scene options. eg, one tap up turns on the lights (via a scene), one tap down turns off the lights (via a scene), multiple taps activates various scenes etc.
If we have a properly configured 3-way circuit with local control enabled, then I can switch the circuit ON and OFF from either end regardless of the other position. If local control is disabled then I have the scene options on the Red switch but the Aux switch becomes a dummy.
What I wanted was for the Aux switch to be able to turn on or off the lights. I mistakenly thought that with local control enabled that the Aux switch was sending some signal back to the Red switch and the Red switch was controlling the circuit. I assumed the same would be true for when local control is disabled but I see now that this would have to be accomplished by activating a scene. It took a moment for me to understand that and it makes sense that this is the explanation.
What I will need to do, if I understand everything correctly, is to replace the Aux with another Red switch and configure it as local control disabled and use scenes.
Thanks everyone for the education. I think everything is clear now.