I cannot see that having happened knowing how religiously Carol maintains her RTAs. An Ultrasonic Bath once a week after a rinse under warm water to get off any residue. She even removed the airflow Screw so that there was NO chance of any gunking up.
The ONLY other thing I keep thinking about, came from another comment that someone else made. He mentioned that he had to periodically remove the Top Cap to release any pressure that had built up? Well, I NEVER EVER Fill ANY Tank to capacity, always leaving about 10 percent empty. It's something I have done from Day One, so perhaps it is worth checking how full the tank is? Can't see that being an issue, but I'm fast running out of ideas.