I can only talk from personal experience after thoroughly investigating the problem of our Samsung TV turning on and off at regular intervals. After trying unsuccessfully with all the solutions mentioned here, it occured to me that this problem has only happened after recently messing around with the router. I would check the 5Ghz wifi settings. For instance, Asus recently enabled DFS channels in the some countries for the RT-AC86U, which might be problematic for some devices. You can try this solution by logging into the router and then either disabling automatic DFS channel selection, or manually configure a fixed, non-DFS channel (like 36) and see if it helps. Reboot everything (routers and TV) afterwards to make sure all the settings take effect. This has worked perfectly for me and a few others I know who were experiencing the same problem.
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