I was writing back and forth earlier today on the Trello board about my own issue with the Weather Underground website. I'll restate it here, as well as another issue that I found which I suspect isn't specific to me.
The problem I mentioned earlier was that ever since the update to the PWS systems and profiles a few months ago, my weather station has not appeared under my account's devices on the website, which also means that the ads have returned. I looked at the mobile app and confirmed that the ads are gone on there and my weather station is registered under my account, so this is just a website issue. I tried resetting my password and email and clearing my browser cache but nothing worked. I also can't edit my weather station currently because of this—I apparently have 0 devices.
The other, unrelated bug is that whenever you view weather station history it works fine for about a year before the current date, but once you go beyond that the graphs fill up with nonsense and way too many data points, so many that it lags the webpage immensely. Screenshots of the graphs and tables of a random weather station supposed to be from May 2018:
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(Also a small annoyance: The graphs don't show up for current conditions for the two weather stations in Antarctica.)
Hope these get dealt with soon, the first problem especially because the ads are maddening.