From GWR’s website:
With rising numbers of staff unavailable to work because of testing positive for covid and having to self-isolate, we have taken steps to maintain services levels across the network, including cancelling all non-safety critical staff training.
Unfortunately, this also includes planned cancellations designed to minimise the impact on as many customers as possible. These are predominantly affecting some of our branch line services in Devon and Cornwall, as well as some long-distance trains. Some services may be busier than normal.
Please check your journey before you leave home at journey-check.com/greatwesternrailway
Customers who choose not to travel can claim a full refund. Please visit gwr.com/refunds for more information