In the stock configuration, the AcuLink bridge does not update wunderground directly.
It's the AcuLink site (MyBackyardWeather.com) that sends data to wunderground.
The first thing I'd check is if the information under "Share my bridge" on MyBackyardWeather.com is correct.
If that's all correct, you'll probably need to call AcuRite's support line as there's probably something wrong with your account.