What electronics and power supply voltage are you using? Missing steps after a period of use could indicate overheating stepper drivers. 0.9deg motors typically need 24V power unless you restrict them to low speeds.
Those motors are rated at 50C max ambient and 80C max temperature rise. So I think it's unlikely that you have overheated the magnets, unless you are using powerful external stepper drivers. If you turn the shafts with your fingers when the motors are not powered, can you still feel the detents?
Those motors are rated at 50C max ambient and 80C max temperature rise. So I think it's unlikely that you have overheated the magnets, unless you are using powerful external stepper drivers. If you turn the shafts with your fingers when the motors are not powered, can you still feel the detents?