It may not be down to ADS-B or FR24.
A couple of years ago I was stunned to see an American Airlines 777-200 and a Kuwait 777-200 flying between Ockham and Biggin at 10,000ft and a speed of 0kts! I am led to believe this is due to the aircraft having INS rather than a more modern GPS based system and it is this that is feeding inaccurate info to the ADS.
I frequently see the same effect at Heathrow when Delta 757 & 767 aircraft show up in Twickenham and then appear milliseconds later taking off right in front of me!
I have seen FR24 show a BA 747 land in Cranford, then taxi up the Bath Road.
Also, at Manchester, I have seen aircraft landing in Styal and on the M56.