If initiation and other devotional activities remove the past karma of devotees, then why do they get diseases and other problems?

From: Neeraj

Prabhuji it is said that at the time of intiation all our past karma becomes zero.Also by taking bath in ganges,chanting holy name,circumulating Tulsi maharani our past karma reduces.Then also we see initiated devotees affected by their past karma in form of diseases and other problems .How yo understand this.