I have the same iMac that you do. I just looked under the Wi-Fi symbol and the list of networks only appear for less than 2 seconds. To view them again, I have to switch Wi-Fi off and then on again.
That's very curious. My list remains in place, although I note that mine keeps searching, so I assume it is working the same as MG2009’s.
When I click on the WI-FI, the dropdown menu will remain visible as long as it is still finding/adding possible networks to join - which, for the area I am in, there are dozens.
When no more can be found - or one is selected - the dropdown menu disappears.
It’s likely that yours is acting the same and the list switches off because it has found all the networks within reach. There is an easy way to check.
When you click on the Wi-Fi symbol, look at the very top of the list. There will be greyed out language that says: “ Wi-Fi: “ followed a message that toggles between “On†and “Looking for networks…â€
However, if you wish to keep the Dropdown Menu from disappearing, you can probably do so simply by pulling your pointer into the list of selections.
