Just saw this article from the Register: https://www.theregister.com/2020/09/18/flight_tracking_adsb_oddity_ins_drift/
tl;dr On 15 Sep 20 G-JOTR was seen on FR24 and stopped showing a track in the sea to the East of Scotland. No one noticed and no emergency was declared. Turns out the ac has a poorly inertial reference system which gives out incorrect data.
FA track for the flight can be seen here if interested (also looks dodgy): https://flightaware.com/live/flight/GJOTR/history/20200915/1446Z/EGMC/L%2056.50929%20-2.33118