From what I understand, they don’t normally bother producing service manuals for individual models. It’s a case of ‘they all work on the same basic principals, so the repair person should be able to figure it out’.
My guess (based on my repair of a couple of aging treadmills that would suddenly jump to full speed!) is that there’s a sensor on the motor that’s malfunctioning and feeding the controller wrong (or no) information. It sounds like it sends power to the motor, doesn’t receive the expected speed info back, stops and tries again a couple of times, then gives up.
This thread may be related (in terms of general info): https://www.diynot.com/diy/threads/beko-washing-machine-motor-problem.616682/
If it is the sensor, they seem to be pretty cheap (assuming compatibility), though I don’t know how easy it is to get the old one off and replace it:
You can still do this in Waterfox, FYI.
I’ve not used Firefox in years (just various forks), specifically because of Mozilla’s insistence on changing the UI and not allowing you to change it back.