Check your battery at the source put a voltage tester across battery. With in ready position what is the blue car display reading . The computer processor supplied by the 12v battery power supply so should there be a voltage problem on that side you will get problems . Let us know readings .
The DC 400- 14.6vDC rectifier charges battery and supplies the auxiliary circuit, this will cut out if rectifier is overloaded by fault on the 12v circuits. A healthy battery is 12.9 v and the blue car display while driving should read a steady 14 v DC.. I've had the computer crashed showing similar faults .get a battery voltage reading with car engine off by an engineer.Auto hold comes in when car is stopped on a hill at for instance traffic lights giving you 3 secs to take foot of brakes to put foot on acceleration to pull off from a hill. If the DC-DC rectifier has been replaced and still having faults. There's 2 things you could have tested that is a 12v battery fault. or a fault on your 400v battery pack.It must be tested by an MG 5 technician. Causing an unstable supply. If the processor was at fault you would have numerous of faults showing on your display intermittently. A high Resistance cable fault is a bad connection or a damaged cable on that circuit.This needs a MG technician only to find it. Hope this helps .A recent MG5 EV software update I had done was involving brakes including Auto hold 4 weeks ago. Ask MG for a detailed report of there findings afterwards. All this comes under your 7 warranty, but been told your 12v battery only has a 12 months warranty.
