As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPEARANCE OF SMOKE/MIST IN CABIN AND COCKPIT WHEN APU BLEED AIR SWITCH TURNED ON. BOTH MAIN ENGINES WERE NOT RUNNING. HAD USED APU BLEED AIR TWICE EARLIER, NO ISSUES. APU OIL HAD NOT BEEN SERVICED TODAY. NO ABNORMAL APU INDICATIONS OBSERVED DURING AND AFTER EVENT. REMOVED AND INSTALLED REPAIRED APU. ALL WORK DONE IAW AMM 49-10-00. OPS AND LEAK CHECKED GOOD.