I found if I entered:
$ nmcli r
I got something like: (I couldn't get a screenshot... a different bug)
WIFI-HW WIFI WWAN-HW WWAN enabled off enabled enabled
Which obviously seemed wrong, a bit more poking with the 'help' function of nmcli and I found I could switch 'WIFI' to enabled by:
$ nmcli r wifi on
and now the the output of 'nmcli r' is:
WIFI-HW WIFI WWAN-HW WWAN enabled enabled enabled enabled
Then wifi worked fine, has persisted through reboots, and is still fine a few hours later. What remains unexplained is why wifi worked (I got a list of visible networks) before failing.
Similar behaviour here.
WiFi stopped working the first time I tried to connect to a network with WPA Enterprise security, and didn't work from then on, even when I restarted. Not sure if the WPA Enterprise part is a coincidence.
I saw "disabled" where your post shows "off" in the output of nmcli r. nmcli r wifi on got it working again. Thanks!