Same or very similar problem on my S8+. I'm using a Tenda MW3 mesh network to which all of my other devices connect just fine. However my S8+ will not switch nodes no matter how much stronger the signal compared with the one it is currently connected to. And for some reason it almost always wants to stay connected to the base node, and will switch to the 2.4ghz band even when the 5ghz signal is perfectly fine. So when I'm in my office, which is through a couple of walls and some 30ft from the base node, it stays connected to that node on 2.4ghz even though the signal is terrible. Then I get the ! like everyone else, and it still doesn't want to switch. edit: forgot to add that if I turn wifi on and off, it will connect to the closest node properly. But as soon as I'm closer to the base node it switches to that and won't let go. So far I have tried resetting my network settings, but this had no effect.
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