As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER APU START AND BLEEDS TRANSFERRED TO APU, THE RPM DROPPED AND EGT VENT WENT HIGH WITH NO WARINING IN THE COCKPIT. APU SHUTDOWN MANUALLY. APU STARTED AGAIN ON GROUND, EGT WENT TO 580 DEGREES CELSIUS AT 50 PERCENT RPM, FOLLOWED BY A 2 METER LONG FIRE FROM THE EXHAUST WITHOUT FIRE WARNING. AWAITING INFO.