It appears it's not app related but Microsofts latest update. Microsoft store on all platforms is affected so any apps or trying to install apps are affected. It seems to be related to US and UK's main internet providers (Comcast and BT). A workaround is to change your DNS settings to something like google dns (184.108.40.206 then 220.127.116.11) but I suppose any other free alternative would do. I had to do it on pc and xbox to get everything working again. I also had to go into my router settings and change the dns settings aswell (google dns). Now everything is fine. BTW it wasn't just Now TV app that wouldn't work or reinstall. Spotify and Netflix also gave me the same issues and they were the only ones I bothered to try so it could be many more.
To change DNS on xbox 1 press xbox button (the one lit up on controller), tap right to the cog (settings), select network settings, select advanced settings, select DNS, select manual, primary dns is 18.104.22.168, secondary is 22.214.171.124 then restart xbox.
If the result is the same as before, like it was with me, then your router probably needs the same DNS setting applied.
Before I did this I couldn't download apps on my pc. I couldn't even run an update check. It would fail. Now tv on xbox wouldn't start. Uninstalled and tried to reinstall but it would fail. Since changing DNS on my xbox, pc and router everything works fine.
It's all well and good to blame the problem on Microsoft but at the end of the day, without the help of yourself and other kind customers, we would still be stuck without the service for which we are paying. Why couldn't someone from NowTV give us the solution? Why have they not got a quick line to Microsoft in case of times such as these? NowTV have instead displayed a deliberately inconsiderate attitude to their customers and I hope others will join me in dropping their service.
Try Manually updating your DNS settings. Just applied the ones below and I'm back up and r.unning.
i had the exact same problem and I thought it was something to do with my Xbox breaking. Then I thought the internet had gone down. But after reading this I feel happier. Thank you for whoever gave us the solution it worked on mine too. Thank you so much