I had issues once and the WiFi scanner app was really useful. Problem I had Was that I could change the channel but the talktalk router would change it back after a short while.
It could also be that the OPs router has a fault with the 2.4ghz and only the 5ghz is working which is rubbish at going through walls.
That is a possibility. Some routers have locked down settings. Over the years I have come across some which, although made by the likes of Netgear, are less configurable
