I bought a TCL 55C725 two months ago. Apart from the OS being a little slow i've never had any real issues with it, until i came home yesterday. I saw that it had updated the Disney+ app, maybe also the system itself. I'm not sure. But ever since that update everything has become unwatchable, everything that i want to watch stops for about 5 seconds after every half a second of playback. This is across all app's: Disney, Netflix, YouTube... There are no issues with my internet, the TV is plugged via ethernet and the speeds are great across other devices. Does anyone know what's going on?
Perhaps rule out the network by trying the Wi-Fi instead of Ethernet. Counterintuitively the ethernet port on most Android TVs is 100mbit but the onboard 802.11n Wi-Fi can reach 300mbit.
Though 100mbit should be ample for 4K content so not confident that's the problem here.
You might want to try a factory reset.