@hindolam 

Channel 153 requires DFS, meaning it shares frequencies with radar systems. If radar is detected, the router must vacate the channel, which can lead to temporary disconnections.

@ArcherC8

In US, (36, 40, 44, 48, 149, 153, 157, 161, 165) are non-DFS channels.It has been working for more than a month without any disconnection. SSID simply disappeared yesterday. I tried to reactivate the SSID again through tether / web. Both these apps showed the 5GHz SSID as being active and the green light on the router for 5GHz also lit.

Finally, I reset the router to default settings by inserting pin into the reset button on the back. Then went through the setup that I had before including the same 5GHz channel 153 and the same SSID name. It's working back again. But this disapperance is really concerning.