I am doing nothing but G commands to control the movement of an XY gantry, and using M106 to turn on a welder on D10, and now hopefully a solenoid on D9. Would D9 having other functions bound to it have this effect, even though I am not calling any other function than M106 P1? I used a multimeter when turning on D9, and got extremely low voltage (enough to just show it turns on practically) compared to D10 which shows 12V DC.
I guess I am just confused on how the D9 pin being bound to other functions would limit its voltage even though I use no other functions that G movements and M106/M107/M114. In the meantime, I will make sure that D9 is only being used as FAN2 like you said