Created attachment 852399 [details]
Partial TB log. From 15:25:51 on, the WLAN has been operational

Reproduction:

1) Disconnect WLAN with KDE Network Manager 
2) Start Thunderbird
3) Wait until it gives the "cannot connect" message
4) Connect WLAN with KDE Network Manager
5) Press "Get Messages" in Thunderbird
6) Expect "cannot connect" message, goto step 5) ad infinitum

The issue also occurs after resuming from suspend state, or on a fresh login
where Thunderbird is auto-started in the background and KDE is waiting for
wallet credentials, before it connects to a WLAN with user specific
credentials. 

Sometimes Firefox exhibits the same problem, however, I did not try to
reproduce this, as for me the issue with Thunderbird is far more annoying. The
problem existed throughout Leap 15.2, 15.3 on this system. I have attached a TB
log, slightly censored for privacy. 

Workaround:

- Restart Thunderbird