Both Unifi and Time broadband provides the default AC router as Dlink Dir-850L. This router is suppose to be using the current Wireless 802.11AC standard which is able to do beam forming and achive higher throughput. Beam forming is a technology where the router is able to focus its power towards the direction of the requesting source, theoratically making the signal stronger (of course the other side needs to have a wireless AC network card also).
Recently I was stump by a hair pulling problem after TMnet came and replace the router together with my Fibre modem. The wired performance was very good but the wireless signal was kind of like moving fast and then slowed down, a bit like a car which was speeding and then had to tap the emergency brakes. The Wifi signal strengh indicator on my phone and laptop showed the signal strength was as "excellent". Running a speed test using www.speedtest.net does not show any visible issues, one moment I could run speedtest and then the other moment when I try to run it it won't work. I tested all the settings like changing the channel, different 802.11b, 802.11g and 802.11n but could not identify the issue.
I chance upon this setting of 20/40 Mhz channel width. I just switch it to pure 20 Mhz range and my Wifi seems ok again. Some people in tech forums are saying 40Mhz channel is too crowded and could be interfering with neigboring Wifi signals. The 40Mhz channel is suppose to be faster because it combines 20 Mhz channels into 1 big network pipe. I didn't thought this setting would cause problems as 40 Mhz is suppose to be ther better setting.