Brushless DC motor problems at high velocities
Normally the motor velocity is limited by back-EMF. Not!



This is false. rather (V-BEMF)/DCR=I, is minimum no load Current and thus Torque is limited by BEMF and max torque ~ 80% RPM/RPMoc or no load RPM
Velocity is limited by commutation errors , Voltage , friction and temperature rise that arises from conduction lossses.
Commutation errors include ringing during dead-time, insufficient dead-time, poor impedance control during dead-time (RC snubber) , excess C with very low RdsOn, ESR, excess ESL in cables, poor high Q switching, **commutation phase error **
for BLDC fans when Hall Sensor has a tiny negative  phase shift, it results in dither or no spin. If positive phase error, less torque, but in your case you have short circuit, so examine torque vs static rotor position at very low voltage (to limit Trise,)if you suspect phase error, or do adj. with trial and error.
With no load, (prop) Max current should be max only at 0 RPM Imax= {Vmax/DCR} = 10x I ( rated max) at full Rate RPM and current at Vmax should be &lt;&lt;10% of Imax at full load with no external,load. This is just surge start current. but at full RPM, these are friction, excitation conduction , &amp; eddy current losses.


So my conclusion is you have a LOT of commutation problems, but the solution will be obvious when you discover the root cause.