i think i have the same problem as u..

My whole family phone when connected to wifi 2.4 or 5ghz,when open youtube,it will loading but need wait for 30seconds for the video to be load...then
I need to turn off my phone wifi and reconnect back to have smooth connection,but after 1-2minits..the problem arise again..need wait 30seconds for video to be load..same goes to instagram...i scrolling scrolling,suddenly it loading and have to wait 30seconds for the pictures to be loaded again..then after few minits..the problem occur again..then wait 30seconds again..then smooth again..then need wait 30seconds again...it like the line sent data to server but the server slow to respond to our phone..all apps is the same..we have to wait a while to get smooth connection,then after few minits..we have to wait a while again to get smooth connection..
my router is rgx4400..do u guys think is router fault?or some settings need to be adjusted?
wifi on laptop no problem,lan cable on my desktop no problem..but only phone wifi got problem..

not yet as i'm working..busy life..
but soon i will call them to replace the router..
it so annoying,i went to my friends house no issue too with their stock tm router..unifi..

Dyson Jin Victor3010
I was at the restaurant that uses the RGX4400 earlier today. Did a test on 2.4Ghz. Browsing seems fine. No stalling that I can discern when loading a website. Speedtests however shows the difference between 2.4 & 5GHz. They're on UniFiBiz 100. Not many people when I was there.

Shouldn't be a load problem. The RGX4400 at the restaurant handles the crowd just fine. Tonight I'd estimate at least 10-15 people were on their phones. It's more crowded at lunchtime and I've never had probs. Dunno what could be wrong. The RGX4400 is 2x2 MIMO btw, i.e.: AC1200. Maybe it's their antennas.