BritBox won't play on AppleTV+

How can I resolve a problem with BritBox? We it watch via Apple TV+ application and for the last week or so the BritBox channel hasn’t been working. It won’t even start but we get a rolling wheel that indicates buffering.

I haven’t found a solution online either. Some suggested uninstalling and reinstalling BritBox but I can’t seem to do that. I figure this tip only applies to Apple TV (the physical device) and not Apple TV+ which is an application. AppleTV+ is up to date so the problem shouldn't be there either.

Apple TV+ itself works just fine, so the problem is definitely the Britbox channel. However, Britbox support suggested I contact Apple support, but I couldn't find any help for this kind of problem.