I assume you are talking about the Billboard text and not about the "other operator logo" that gets drawn below Billboard if that option is chosen (the "other operator logo" is indeed limited in size by Billboard to avoid screen burn-in).

If it doesn't work for you even after reinstalling the app and making sure the .css file has been properly updated (and fully restarting the device without any charger connected, then waiting a few minutes for Billboard to start up from a cold start), you might need to re-flash your firmware from scratch. Some applications (especially the tweaking applications, which already state that you have to be careful when using them in the description) might mess up the configuration in a way that isn't handled by the Billboard installation routine.

Installing Billboard on a freshly-flashed device always worked so far, so that's the only known-good solution that I can provide here. If you happen to choose to go that route, please note which other applications you also install, so that in case Billboard breaks again in the future, we know which other app is causing the problem.