As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAKEOFF ROLL AT 50 KIAS, RED "HDG" FLAGS APPEARED ON CAPTAIN PFD, MFD, AND SIMULTANEOUSLY ON STBY HSI. AFTER 15 SECONDS RED FLAGS DISAPPEARED AND HEADING DATA WAS ONCE AGAIN AVAILABLE ON SAID INSTRUMENTS REMOVED AND REPLACE NR 1 DG IAW MM 34-21-05. OPS CHECKS GOOD.