The altitude is definitively incorrect. It just passed my house on a lower altitude level.
Seem to be a misconfiguration in ADSB data
Same on other flight sites.
Landed in Frankfurt again. Seem to be an emergency, the approach direction from west doesn’t match to the current approach in Frankfurt.
All other aircraft approaching FRA at this time needed to run in a waiting loop
Now it is clear.
The aircraft had a technical failure right after the start which gave the crew useless data about altitude, speed etc.
The captain sent a “mayday, mayday” and returned to Frankfurt immediately after dumping fuel