Google Nest Community

Sorry, couldn't resist...

Have you actually tried moving the TV closer to the router?  

Sadly no, that'll break it again. I wasn't going to give it a couple of weeks before I try it again for Talktalk to hopefully acknowledge they have a problem and fix it...

Got it! At the bottom of the Home screen in the app, go to 'Security and Privacy' and disable 'Advanced Security'.

Just to add, I've tried connecting to a hotspot on my work phone and everything worked perfectly. Eero and/or Talktalk is definitely the issue.