pylon:
Yes. And remove all Serial stuff from all interrupt routines.You should tell us if you use another type of Arduino than the UNO. Without any mention of a special type we expect you to use an UNO.
I stated it in my opening question right before the code.
Delta_G:
Button presses are ssssssllllllloooooooowwwww. Totally not something you should use an interrupt for. Just poll the buttons from loop.
Yeah thinking about that to. I think the MultiStepper and AccelStepper use interrupts for the timing, so my button presses don't come through anyway all the time.
gfvalvo:
That is not your complete code. Where is the variable 'steppers' defined?Accesses of the 'mode' variable may not be atomic. They need to be protected from interrupts in non-ISR code (i.e. loop()).
Sorry, i cut something off there. What do you mean atomic?