anyone experienced this at all.

Motors were working fine and now nothing.

They twitch on startup but won’t spin.

Is there a way to diagnose  what’s wrong

Two possibilities, faulty motor or motor wiring, defective ESC. Motor two is front right BTW. if in warranty send to DJI otherwise open it up or have someone do it for you and look for wiring damage. To investigate further will require the motor disconnecting, soldering job & replace the arm and motor as this is the cheapest option.

Looks like you will need to return to DJI for repairs.

Same problem here, https://forum.dji.com/forum.php?mod=viewthread&tid=97544 diagnosis damaged motor coil, if no physical damage noted in the motor you probably have a defective ESC. I would try to refresh the firmware to see if that helps.

In you situation, please contact our support and send it back for repair: http://www.dji.com/support Thanks for your support.