That doesn't help. The plastic part inside the switch will give up when the hours are full :(
Stick a toothpick between the button and the casing to lock it down if you want to be sure..
(..or solder a jumper to the circuit board.)
Same here (RT-AC66u H/W Ver. A1. SN:C7IE0B002922), the switch just released by itself after some 2 years and did not stay in any more.
Seems to be an obvious material/component defect. Hopefully someone from Asus product development reads these and invests a few cents more for switches in the...