That was ... interesting. The Wi-Fi Inspector stopped working. Going to it, it was always showing the result of the last working scan (which I closed each time, so it shouldn't have been going back to it), and closing it and asking it to scan again, the scan opened and the scanning animation started, but it just remained stuck at 1% and never showed anything on the network, and cancel just caused an endless cancelling animation. Oh, and while - when it is working - it finds the laptop, router, Android phone and television, it doesn't appear to be able to see my Kindle.
The Wi-Fi Inspector problem
might have been triggered by some of the Firewall settings changes I'd been making while trying to nail down some firewall bugs and/or bad design I've run into while finding why it wouldn't allow Miracast (and no firewall settings should trash the Wi-Fi inspector); and it only started working again after I uninstalled the Wi-Fi Inspector module (then had to reboot), then reinstalled it (and had to reboot again) while also changing some of the buried Firewall settings again (shouldn't have done them both at the same time, so left me unclear exactly what got it going again). Not exactly robust design.
This Firewall business ... OK, maybe only a minority of Windows 10 (and

users ever want to screen mirror to a Roku box (or other screen), but it shouldn't take settings hidden in the 'Old Settings' or the 'Geek:area' - and settings whose avowed purpose is something different, and which open a potentially dangerous vulnerability at that. Using the Miracast Connect feature of Windows 10 might be something only a few users do, but the Firewall should allow for it properly: this is a real mess.