@andrea_104kg - blue cog was ok, and I suspect the internal bearing is ok. Ordered metal one and a spare blue one, and there's no change. Chinese vendor not much use - timezone, language, etc. Put the motor into test mode for torque, and readings suggest its ok. But I get no power assist. Feels like the motor is trying to do something because it sounds different. Options ... one way bearing (I understand this is more to do with pedal slippage though) or PAS sensor. Supplier did ask that I move the speed senor closer to the magnet...my issue with this is I've done 1300kms and no issues.
I do believe the motor is fragile, and to have reliability you almost need to stock at least one of each part. I was quite attracted to the ideal of this motor ... but its just not robust/ reliable enough. Will continue to try different options to fix.
In the mean time I've bought a Giant e Pro 3+ ... was 20% of RRP - its a nice piece of kit, and hopefully reliable. No real difference in power, but more refined - quiet, low temp, and smooth.
Regret going down the Tongsheng path as a commuter...you pay for what you get I suppose.