6. That is just Unifi DNS redirect you to their website if the your DNS query yield no result.

You shouldn't use 40MHz on 2.4GHz band unless you're on landed property with very few neighbouring networks. And never ever force it to 40MHz on 2.4GHz. It will help with the bandwidth when there is no neighbour communication on the extension channel.

Could be your heavy user neighbours already went for holiday and thus less interference. If possible, log the ping to a file continuously for few days after they are back. Strong neighbouring wireless network won't cause much interference if there is no traffic on those network. It is those network with non stop heavy traffic that will cause more interference if the signal is strong enough.

My neighbour all old hang or just 30s plus that lessly use internet.
I switch to 40MHz and experience better ms rate and performance to my RDP (Malaysia to Malaysia Server, the Server original host on US, so it's Me to MY to US) Better response.

But often get disconnect in the afternoon.

So I switch it back to 20MHz