If you're using Google Chrome, I've found a fix: (It'll also work in other browsers, you'll just need to modify the instructions to find out where you can delete site data and cookies)

Go to chrome://settings/

Search settings for "cookies" and then click the highlighted content settings, and then cookies

then click "see all cookies and site data"

then where it says "search cookies" type catanuniverse

then click the delete on all of the search cookies things

Now, you'll be logged out and able to log back in, and it'll be in online mode

Just tested now, December 5th 2017, on the latest version of Google Chrome, and it works great.

@whuffo Good point, it does seem plausible that you get both of your players in the same game with a window of 1 or 2 min, possibly even less.