I SOLVED IT! I had this exact issue. Not sure if you ever figured it out but here is the solution.
These switches on the Alpha are technically two buttons in one. When you move the button into the upper position (on) its like pressing and holding button 17 and when you switch it to the lower position (off) its like releasing button 17 while now pressing and holding button 18 (which is what the lower position is).
Find "Electrical Bus 1 to Avionics Bus 1 ON.
Make sure the bus 1 switch on the yoke is in the lower (off) position.
Click to set the keybind and when it says “scanning” you flip the switch UP then DOWN (on then off)
It should now show that “Joystick Button 17” is bound
Now, for the very important step! Turn that same switch now into the ON position!
find “Electrical Bus 1 to Avionics Bus 1 OFF”
Click to set the keybind and when it says “scanning” you flip the switch DOWN then UP (off then on)
It should now show that “Joystick Button 18” is bound.
Repeat this for the Bus 2 and both switches will now work as intended. I don’t know why this is necessary for only these switches and the ALT and BAT switches dont need to be set like that, but it works, so whatever.
It was bothering me for so long! Hope I was clear enough! Keep this in mind too when setting other switches. Sometimes if it doesnt work, maybe this method may be necessary.
NOTE: There is a bug when you bind those specific actions though. If you have a bravo throttle quadrant and you bind those two actions to ANYTHING, then the plus/minus knob (bug) only moves in increments of 10, rather than 1. Unbinding those two settings (electrical bus 1/2 to avionics bus 1/2) fixes this, but now you can’t use the switches on the Alpha to turn them on and off. This has been an issue since 2020. They fixed it once, but as usual for Asobo, the bug has returned. If they just made any of the NON-AIRPLANE SPECIFIC settings turn on and off the nav switches in the Cessna, then this would no longer be an issue.