I just bought a new wifi repeater. It's a Netgear EX6120. I'm using a Pi 3 Model B+ to configure it with its web browser, since I couldn't get WPS to work. I have managed to connect to its configuration page on the NETGEAR_EXT net and have configured the repeater. The repeater seems to be working - my main router reports two new devices in its WLAN client list, which I presume are the repeater's 2.4GHz and 5 GHz connections, and I have been able to connect my phone to the new MYSSID_2GEXT net that the repeater is serving. The lights on the repeater are also as expected, with green for router and power and WPS.
But the device light is off on the repeater, and the pi 3B+ has no networking
I've been unable to get the pi to restart its networking and am looking for help with that.
I need (well desire) to restart the network without rebooting the pi, because the repeater's web page is still open on the pi's screen and I am supposed to click on that page AFTER restarting the pi's network with a connection to the repeater's MYSSID_2GEXT net, in order to complete configuration of the repeater.
I have tried various things such as sudo ifconfig wlan0 up and sudo systemctl restart network.service and I've made sure wpa_supplicant.conf looks sensible. But the network widget says 'eth0:stopped wlan0:stopped' when I hover over it and 'No wireless interfaces found' when I click on it. sudo iwlist wlan0 scan shows the original nets from the router and the new nets from the repeater though, so clearly the network hardware is still actually there and working.
Since I don't have a working network on the pi, it's a bit difficult to provide content of files or output from commands, hence the sketchy details I've provided. (I can't restore the ethernet connection because it conflicts with the repeater's setup addresses.)
Can anybody suggest what to try, or point me to an up-to-date how-to on troubleshooting wlans on pis?