Google Nexus 7 2013 (6.0.1) no longer works with All 4 streaming (UK)

I have a venerable Google Nexus 7 2013 (OS 6.0.1) that I still use. It works well - or did, up until a few days ago. One of the things I use it for is streaming - BBC iPlayer, ITV hub, All 4, youtube etc. It has been fine up to now, when all of a sudden it will not stream All 4. It will stream everything else and all other internet connectivity is fine. The local network is wifi (2.4/5GHz) connecting with a TP-Link ADSL router to Plusnet Fibre. Initially I though it was a temporary All 4 problem. But other devices (Android and PC) on the same network stream fine. First I restarted the app, then cleared the cache and data, then restarted the router, then I reinstalled the app, then finally I did a factory reset. None had any effect. The error is 'An error has occurred - Touch to retry'. Retry has no effect. Unfortunately I do not have access to another wifi network I can try. I am completely out of ideas. It must be software, all hardware appears fine. The summary is: - Nexus 7 2013 running Android 6.0.1 (not rooted). - Will not stream All 4 (UK). - Will stream everything else. - All other internet connection is fine. - Other devices (PC, Android) on the same network will stream All 4. - Resetting everything had no effect. - Worked fine up to 7-10 days ago. Any suggestion as to the cause of this would be welcome.