External roller shutter not working properly - RST-3D controller or motor?

Hello,
with me, one of the eight external roller shutters has stopped working. It doesn't respond to presses of the switch (two-key switch). Before the fault it was the case that momentarily pressing the key caused the roller shutter to move up or down. Pressing the key again stopped the roller shutter. At the extreme bottom and top positions, the roller shutter was stopped by the motor stops (I don't know what motor it is). The roller shutters are controlled by RST-3D controllers located in the electrical switchboard. At the moment, one roller shutter is not working. I switched off the power for a while and tried if the roller shutter would work after switching on the power. The motor works, the roller shutter can be raised or lowered, but in short strokes. It goes a few cm with each key press. There is no continuous movement after releasing the key. I managed to lower the roller shutter and that was it. To raise it I had to switch off the power again for a while. And so it goes on. Could someone knowledgeable tell me (maybe they have encountered something like this) whether it is a faulty RST-3D controller or motor.
I should also add that the roller shutters are connected to the central control and this roller shutter does not work, the other 7 work.

Unplug the wires from that roller shutter from the controller and apply power, this will tell. My bet is that the motor is working.