Hi,
I unlike Peter think its a noise problem. It is electrical noise that is intermittently triggering you limit switch circuits, and that same noise could easily affect one or more stepper drivers.

How have you routed the spindle cable? You need to have it separated from signal cables as far as possible Where they cross each each try to ensure they cross at right angles. Any time
a signal cable is lying along side and parallel to the spindle cable is the opportunity to contaminate that signal.

Craig