The ghost sector is left to assist with any refunds. PNRs get recycled (and I've had one PNR twice over separated by many years for 2 completely different bookings) and the data gets deleted with a few weeks. If BA's back office has a backlog of cases - which seems to be the situation for half the year - then it helps them to find all the relevant information if the sector is left in the system, cancelled, but forwarded dated so as to prevent deletion.

For the OP, this may be solved by logging out and relogging in, or even signing out and re-installing the app. But my best guess is that it will slide away in the next few days anyway.