Why does the number of threats stopped go down?

"On TrendMicro, the list of "Threats stopped" in the past month sometimes goes down rather than up, sometimes by a huge amount in one day. Could this signify a threat that was previously thought to have been stopped but now isn't? Why would it do this?"

This is the normal procedure of this product. It consumes lots of cpu potential and slows down the process. you may use Trend Micro Smart Protection Network for better performance. Also it depends on RAM/Process speed/network bandwidth etc. you may link here to clear the concept, specially on TroubleShoot Chapter