It would seem that the laptop I name ‘Klystron’, is befallen by not one but two WiFi problems, which made it hard to identify either of them.
The main problem I was trying to get a handle on as late as This Posting, could be described as having a WiFi status that seems active to programs running on the affected laptop, but which causes that laptop to seem to lose its connectivity with the rest of my LAN, as seen from the LAN. I can verify that within seconds. It seems to take place, whenever I just close the lid.
The previous posting combined this observation, with the fact that I had set the Lid Close Behavior to Lock the Screen, to suggest that maybe the Screen Locking function built-in to KDE, was triggering this situation somehow.
But what I have now done, is to change the Lid Close Behavior to Turn the Screen Off, which simply causes the backlight of the screen to go dark. And just as before, closing the lid causes the same condition. What this rules out, is that the problem was caused by the KDE Lock Screen function per se. Further, KDE can be told to lock its screen, just with <Ctrl>+<Alt>+L. If I enter that key-combination and keep the lid open, ‘Klystron’ stays visible to the rest of my LAN, and its WiFi appears unfettered.
Now, what can sidetrack this, is the fact that a second type of malfunction will sometimes set in, which actually causes its WiFi to seem to log off, and which requires that I reconnect. One reason for which I need to reconnect, is the fact that my WiFi passphrase is stored on the laptop in a user directory, but as part of the KDE-Wallet system, that keeps such information encrypted with another password.
Hence, whenever I want the WiFi to reconnect for any reason, I must first unlock my KDE-Wallet, so that the Network Manager can be given my WiFi passphrase, to reconnect.
It is not clear what causes the initial disconnection though. A part of me thinks this could be due to misuse of my laptop on my LAN, of IPv6 addresses. But another part of me thinks this could be due to dodgy support of 802.11n within Linux drivers.
What I do know is that this second problem sets in much less often than the first.
Also, it is possible that closing the lid does not physically sever any type of antenna-connection, but may rather change the geometry of the antenna wave patterns, so that the signal strength may just go way down. This may be confirmed at some later point in time, when I try moving the laptop to a different location, relative to my router. I just find the thought sad, that there might be some sort of more-serious, hardware issue with the WiFi, since hardware issues are finally harder to solve than software issues.