Exact same error for days here. The end result is my overlay info is not updating. Acts like it is being refused a connection to WUNDERGROUND. Dunno. Just a SWAG on my part.
Upgraded to 5.3.2.6 today and immediately had the same exact issue in the UI3. I got the popup and just as it started to fade the popup would refresh itself. tried a different streaming quality but no good. Reverted back to 5.3.2.5 and all is good again.