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When the 5G channel disappears, how far from the wifi router are you? The 5G channel doesn't travel as far as the 2.4G channel.
You should make a new post now so a moderator will look at it. Include that it is not a distance issue.
It could be a faulty TP Link router.
Sounds like @david64 might be right.
Could you please send me a PM (private message) with your Full Name, CID (customer identication number) and your mobile phone number, so I can take a look at your account?