overbooking
On 22nd OCT LHR-DXB 004 - First class is fully booked and Business class is overbooked, may be that's the reason.
Actually all 5 flights LHR-DXB on 22nd - Business is overbooked, 002 and 004 FC is fully booked, 006 and 008 and 030 two FC seats available on each flight