From the FGW website :

06:15 Oxford to London Paddington due 08:09
This train will be terminated at Reading.It will no longer call at: Twyford, Maidenhead, Taplow, Burnham, Slough, Langley, Iver, West Drayton, Hayes & Harlington, Southall, Ealing Broadway and London Paddington.This is due to a train fault.

07:10 Oxford to London Paddington due 08:21
This train has been revised.It will additionally call at: Didcot Parkway.It will no longer call at: Cholsey, Goring & Streatley, Pangbourne and Tilehurst.This is due to an earlier train fault.