I gave my 2.4Ghz and 5Ghz channels different names so I can see which channel my devices are connected to. My Amazon Fire HD tablet and Samsung A5 2016 phone both connect to and sit on the 5Ghz channel and when I'm downloading big files I hear the 'crackling' sound from the router's 5Ghz but sometimes my phone connection slows down and only gives the throughput (speedtest.net) I would expect in 2.4Ghz mode (40/20 2.4Ghz, 80/20 5Ghz) I've tested this with both devices only a few feet away from the router. Scanning the 5GHz band where I am I can only see my router on channel 44 as opposed to a lot of congestion on the 2.4Ghz band.
The only way I can seem to fix things is to keep bouncing WiFi on my phone until I get back to 80/20 mode. My other phone acted the same.
Has anyone else noticed this? and did you find anyway to better deal with it?