I've had this problem before when using Manjaro KDE. I'm not sure if it's a kernel problem or if it's a KDE problem. The problem happens whenever I disable WiFi connection or if I enable Airplane Mode from the System Tray. The only way to fix this issue is by restarting the Network Manager via SystemD. Linux/KDE Plasma: Kubuntu 18.04 LTS KDE Plasma Version: 5.12.8 KDE Frameworks Version: 5.44.0 Qt Version: 5.9.5
Can you check if NetworkManager is still running? What does nmcli d and nmcli c show?
(In reply to Kai Uwe Broulik from comment #1) > Can you check if NetworkManager is still running? What does nmcli d and > nmcli c show? 1) $ nmicli c (before) NAME UUID TYPE DEVICE MyWiFi random numbers wifi wlp3s0 $ nmicli c (after) NAME UUID TYPE DEVICE MyWiFi random numbers wifi -- 2) $ nmcli d (before) DEVICE TYPE STATE CONNECTION wlp3s0 wifi connected MyWiFi enp5s0 ethernet unavailable -- lo loopback unmanaged -- $ nmcli d (after) DEVICE TYPE STATE CONNECTION enp5s0 ethernet unavailable -- wlp3s0 wifi unavailable -- lo loopback unmanaged -- 3) I recently asked other kde users and they claimed to have the same problem. I've been having this problem since 2016 and reported it. I barely disable my internet connection and hence didn't know it was still an issue.
*** This bug has been marked as a duplicate of bug 400535 ***