Hisense U6G Apps Not Working

I've seen similar with roku TCL and Hisence with sling and hulu apps from time to time. 

A few things can happen.  1st one is there seems to be a memory leak on TCL and Hisense TV's, so they exhaust memory eventually.  They might even reboot on their own.  From Settings, reboot the TV then launch your app.  See if it helps.  

Another one is bandwidth issues -- I deliberately throttle streaming devices with a firewall to cut down on data usage.  Hulu is kind of a data pig.  There's a bandwidth setting on the TV too, although I found it to be pretty inconsistent and even non-functional with some apps, which is why I do it with a firewall.  It will always upshift to 4K if it can.  If you set the bandwidth low on the TV, you'll get network errors when it tries to play a commercial that only has a high resolution stream.  The other thing that can happen is that if you don't have the restriction set on the TV, it will play everything at the highest resolution it can pull down the pipe, until it can't due to network conditions, then throw the error out of the blue.  It's another reason why I throttle streaming devices.  Smooth out the playback so it's not bouncing between stream rates all the time.  

The TV also reloads the apps when you launch them.  It will offload the app to save memory if you switch to other apps, then switch back.  If that stalls, the app can become corrupted.  It's kind of a bummer, but just delete the app, then download it again.  You might have to do that if the app refuses to load as well -- another condition I've seen.  You'll have to enter your username and password again, and also on all Roku's you have setup (it wipes the app out on them out too if they're on the same Roku account).  A clean downloaded copy usually fixes it.

Try the TV reboot and messing with the Bandwidth setting on the TV first.