Well I'm a senior software engineer so know my way around apps so hopefully it wasn't user error. I've also been using the GWR app since it came out and at one point led a tender to replace it (sadly we were unsuccessful).Are you sure the app showed no trains? If it didn’t it was most likely a technical issue rather than intentional, the app should show the strike timetable, as every other journey planner.
I know it was showing Bath - Bristol journeys earlier in the day, so would be highly surprised if it didn’t show Chippenham. It seems to be showing them for Monday too.
I'd been looking for 3 days prior and tickets were available in the days leading up to Saturday but as soon as the date was set to Saturday a message was displayed saying no tickets available for this journey. I was wondering if it was an attempt at capacity management . Anyway over and done with but I thought it was a classic example of miscommunication. It did make me question the other apps and websites and we arrived at the station almost expecting it to not be running (if I'd not seen it leave Paddington on RTT).