On your remote, press STAND, >

Seriously, though, almost all such issues lead to the answer, "re-orient your antenna".  Particularly telling in your case is that the 5GHz signal disappeared while the 2.4GHz one is still visible: the higher frequency has less wall-penetrating ability than the lower one.  

Of course lots of things can *cause* the signal loss, including weird stuff like placing a BeoSound 1 or 2 near the Wi-Fi access point, your neighbor turning on another Wi-Fi gadget and forcing your access point to re-assess its "automatic" channel choice (which setting is often the cause of problems, by the way), etc. etc. etc.  Rarely is the problem with the receiving device hardware, per se -- and "nothing changed" is tough to guarantee unless you live out on a farm somewhere. 

To test if I'm right or just blowing smoke, simply drag your Wi-Fi wireless access point out of its closet and plop it down as close to the Avant (unobstructed) as possible.

Thanks

Doesn’t seem to be problem with the position of the wireless AP. It is found when the TV searches for the network and has adequate signal strength. But after moments of “connecting...”, it fails with the message “could not find your network” coming up. I have several other devices including other beovisions connected to the same network. 

Not sure if this might be a known software/firmware problem or I should try and reset the TV?