I have seen many boards like this one on youtube working, I wonder if they had your problems.
Most of the Chinese boards have this problem. It actually runs little better at 12V (without above fix) but problem increases as you increase the voltage and speed is pretty low. I'm now using my boards at 24V without problem. :-)
Two other problems have also been identified in these boards, which I forgot to mention.
1. There is no EMF protection diode in motor relay. It can cause to break the on-board 12V regulator. Solution: add a diode in parallel to relay coil.
2. Insufficient heatsink for 12V regulator. I haven't measure the temperature but it is untolerable. Temperature was normal when I just disconnected the driver fan. Solution: disconnect the fan and connect to an external source.