It's a small point, but BA only has two flights a day on this route. The earlier rotation (BA207 LHR-MIA and BA206 MIA-LHR) operated as scheduled, albeit that the LHR-MIA direction was delayed (like other airlines' flights that morning).

Notably, the later rotation (BA209 LHR-MIA and BA208 MIA-LHR) was cancelled at 0551 GMT/UTC on 3 March, ie more than 8 hours before the scheduled departure time of the flight. This suggests that it wasn't some last-minute difficulty at LHR that caused the cancellation.

Idly flicking through the flown itineraries of the A380 fleet, it did cross my mind to wonder whether G-XLED unexpectedly went sick for a couple of days, leaving the fleet one short.