This flight: flightaware.com/live/flight/N505 … Q/tracklog has strange altitude reporting towards the end of the flight. It makes some improbable trips from FL350 to FL200 or so and back. Aerobatics or tracking errors?
Search the forums to find other flights with similar quirks… it’s an error in the FAA’s system where a second radar facility (not the primary one tracking the aircraft) will report the aircraft is at its recently or previously assigned altitude.