Giallo Corsa
Well, if the TV works fine whenever connected to your phone, and you believe that your router is good, you could have been facing problems with your isp or router configuration. Maybe you're blocking some ports on your firewall that the tv is trying to use while connected and the tv is "frozing" when not being able to reach the destination.
Here is the deal. Test the tv a lot on your phone, see if you can replicate the problem, if not, the first thing to do is to try any media sharing with the tv over your network, with the wan cable disconected from the router, to see if the connection is stable when using the network adapter, but without internet service. If everithing work flawlessly, I mean, if you could watch some good minutes from any good quality movie, and can seek without problems, drops or significant hiccups, your tv and router are good.
If that's the case, you should monitor your network traffic to see if there's something happening when the tv sops working. Like if it's trying to access some specific ip's or if there's some tentative to communicate with some server over a blocked port on your router firewall. You could also disable your router's firewall entirely just to do some testing (and please, remove everything else from your network while doing so).
The way you described it made me believe that everything is right with your tv.
Please reach out if and when you do the tests. I hope you can figure it all out.