Loosen your motor mount screws a bit and check if there are any sparks inside the motor
If there is a circlip on it just take that off with some pliers then the motor can should pretty much fall of and you should be able to see the stator and wires if there are any shorts. If there is no circlip I am not sure how to get it apart
What @grecoman said - It’s possible that the motor mount screws are too long and are pressing against the internal windings, causing a short. Try loosening/removing the motor mount screws and see if that helps.
Seems like there might be a tear in insulation and one of the phases is touching the motor body The short seems to be happening with movement, not consistently which is what you would expect with a constant short like a screw.
Mount screws are the perfect length actually. Nothing sticks out the end into the motor (have washers to prevent). I have taken apart and verified that but it was initially on my mind!
I will check all insulation. This definitely could be the cause - very intermittent shorting but no sparks that I can see while this is happening. Might also cut all wires 1cm shorter and solder new connectors in case something else is the matter…
Internal wires all look ok though, once it gets past the sheathing. No broken wires and windings are nice and tight.