My tv has the same problem. After around 30-40 minutes of watching anything, it will blink a few times then just give up and disconnect and it's hopeless after that for a number of hours. It does always eventually come back online on its own after some time? None of the offered solutions ever help in the moment though. The tv is unresponsive. Everything's been reset, plus I just got a new modem-router this week, which can handle up to 6gb, it's not the wifi, etc.
At least for my tv the real giveaway is that it doesn't just drop MY particular WiFi's connection, it suddenly can't find ANY wifi signals in the area anymore. This happens in the middle of streaming something - something it would've required a signal for not 5 seconds ago. And now it cannot even detect any wifi signal in the nearby vicinity anywhere. I go to settings and check connection, and it can't even come up with the list of local networks around my house. Nothing. Not connected. Not connect-able. All my other devices are absolutely fine, unbothered, working well, no signal issues.
I missed the last 30 seconds of the ball drop this new year's because of this 😞
This definitely seems like Roku's fault somewhere along the line. To me, this appears more like a hardware or the Roku device's specific software issue, rather than a WiFi or range or connectivity issue.
Could it be a cache piling up with junk somewhere inside my tv's software and that's why it requires a shut down and cool long? I don't know.
I've seen other posters in other threads mention possible communication between the Roku device and the router seeking an "AFK" response to see if the device is still being used/is still active, and that's what makes it cut out like this after a period of time. Here's that answer if you want to check it out and see if it helps you: https://community.roku.com/t5/Wi-Fi-connectivity/Loosing-internet-connection-and-everything-else-in-the-house-works-still-except-the-roku/m-p/676028/highlight/true#M14944
My only other guess is that it's a planned obsolescence feature, not a bug.