The help count you see in your team shows the number of helps you have given in the last 7 days. Since the number of helps you have given 7 days before is higher than the number of helps you have given yesterday, the overall count decreased even if you helped your teammates.

For example, if you help your teammates 20 times a day, you will have an average of 140 helps in your help count. If you help 10 times the next day, your help count will reduce to 130 even after helping, as the data of the 20 help you had 7 days earlier will be removed from your help count.