Hello @HsinSWT ,
When i see results like this, i would say there is probably 90% chance that the motor is bad. Unfortunately, there is a chance that the ESC is bad as well, and there is no good way to check the ESC without a known good motor (however the ESC failure is unlikely).
As I mentioned in the previous post, if you had a milli-ohm meter, you could test the motor winding resistance to confirm whether the motor is good or bad. A tool like that measures resistance with high precision (similar to a regular Ohm meter). However, if you don't have one, it may not be worth buying it..
You will not be able to measure the winding resistance of these motors correctly with a regular Ohm meter. However, you will be able to detect a complete open circuit (which could be the case, maybe worth trying). If testing resistance using a regular Ohm meter, any two connections between the 3 motor phases will read 0 ohm (or close to that). If a wire is broken, then you can detect it.
The Starling 2 motor (3000kV) has around 0.360 - 0.370 Ohm phase-to-phase winding resistance.
In order to confirm that the ESC is working properly, you could temporarily connect one of the working motors to the ESC Channel 0 and do the same spin test (using voxl-esc tools), just to confirm that the ESC Channel 0 is working fine.
In order to fix the issue, you could order a new motor and replace it yourself (will be a lot cheaper): https://www.modalai.com/products/starling-2-replacement-parts?variant=49707605393712
You could also send the whole drone back for repair (https://www.modalai.com/rma)
Alex