Upvote:3
After finding time to ring Emirates, I eventually got my answer!
There had been a minor schedule change on one of the returning flights, which meant the connecting time in Dubai no longer met the Emirates minimum connecting time of 75 minutes (which I read about on this SE question). For this reason, we had been automatically moved onto the considerably earlier flight.
Looks as though the online booking/eTicket not updating may have been a technical issue though (alongside the lack of emails informing us about the schedule changes), as this needed to be updated manually by a member of staff.