I have a Zyxel AMG1302 router which does this with an Android tablet. All Windows pcs see the router, but on two occasions the Android refused to see it.
It's not an Android problem as such, because it will see other routers appear and disappear as they are switched on and off.
This has happened twice in six months of daily use. On the first occasion I reset the router through it's firmware. When it happened yesterday I tried a simple paperclip reset, which cured it. Either will set everything back to defaults, which is a minor bore if it's just the SSID and password, more so if it's set up to do clever streaming etc.