schilke It might have switched to a channel your Mac would not 'see' (/receive).
If your BT Hub is set to automatic for channel selection (a common default setting) then it may have found other signals on the channels it would use, some of the time, and therefore go down the list to less popular channels.
As I indicated in my post on 19/12, if my router is on certain channels my iMacs act like there is no signal whereas my Android mobiles all 'see' it and can use that connection. I was manually setting the channel to avoid interference with routers from neighbours on channels 1 and 6 (two very popular starting channels for most routers from what I have seen).
Of course, for the router, once it has found signals on channels 1 and 6 (from neighbours) it may go on to choose a channel which my iMacs would not be happy with, and while the router and Android phones are all happy, the iMacs would just sulk and claim there was no router to connect to...
Clearly, when someone uses the default settings (so wireless channel is 'automatic'), the actual channel used each time the router restarts is dynamic, as it will all depend on whether neighbours have their routers on or off, and if on, how strong their signals are as 'seen' by your router.
If you check the diagram on *> Wikipedia