Dear elkaybe, Blick, and WeatherCat troubleshooters,
Let me also welcome you to the WeatherCat forum!
I have a Davis Vantage Pro2 with Mac running 10.12.2 and WC 2.4.1.
I lost communications with WU about 2 months ago.
Since then I have updated WC and OS thinking that would help but it didn't.
. . . .
It occurs to me that the time you mention was a period when Weather Underground was updating their databases, and at the time, they changed the criteria for passwords. Some passwords didn't meet the new criteria and fell into limbo. You might try to reset the existing password on the Weather Underground website and replace it with a password that meets the new criteria. If you put that new password into WeatherCat that might solve your problem. It has for other WeatherCat users.
Let us know what you discover!
Cheers, Edouard