With the ~month long Chinese New Year going on I wouldn’t expect a response until mid-late Feb.
As far as we can tell, it’s only the hardware configuration part of the firmware that was changed. MakerX changed the shunts on this unit with lower resistance ones so they run cooler. The firmware just needs that resistance value to accurately measure the current. The other change is to raise the maximum allowable current limits compared the regular VESC 6 firmware.
I think when they posted the 5.3 binary, they accidently uploaded the 5.2 binary, or compiled it incorrectly.
Two people (that I know of) are running this custom 5.3 firmware and haven’t reported anything strange.