From the FGW website :

Line problem between Reading and Didcot Parkway.

Train services between Reading and Didcot Parkway are being disrupted due to a broken down train. Engineers are working as fast as possible to restore services to normal. Short notice alterations and delays of up to 30 minutes can be expected.

Train services out of London Paddington are currently unable to call at Pangbourne. Customers travelling to Pangbourne are requested to change at Goring.

10:00 London Paddington to Oxford due 11:30
This train has been revised. It will no longer call at: Pangbourne.This is due to a broken down train.