I have two Roku TCL TV's. On both of them, once in a while, when I turn on the TV, the WiFi is disconnected. This doesn't happen every time.
Sometimes, simply doing "Check connection" fixes the problem. Other times, the "check connection" option is not available, so I have to set up a new connection (but it remembers the WiFi details).
My WiFi is stable and never disconnects when I'm watching the TV. This only started happening a few months ago. I'm using Google WiFi routers and get about 80mbps.