Oh. Maybe something is shorting out and tripping the BMS? Electrical tape is highly suspect. I would never use that. The tape will break down overtime and become a sticky mess whenever you need to work on it.
I’d think that if it was a fault with a component, say ebrake, pas sensor…etc, you would get an error code. Since the whole bike shuts down, I’m guessing a metallic fault.
If it were my project, I’d start by disconnecting the cable from the controller that goes to all the other devices, disconnect those devices. It’ll be easier to identify faults with the cable open at both ends. I’m assuming this is a 9 pin plug at the controller. Probing each pin will be tedious, but seems necessary in this case. A used bike, with shady/vague history deserves a complete over look at everything, mechanical and electrical.