Decreasing comments counts on Google Play

My app is loosing comments. Rate number went down 5 in 2 days. Does anybody know why it happens?

Did you get those reviews by review exchange?

Yes i got some of them by review exchange

That could be the reason, maybe Google is not counting reviews that are written just after the app is installed or reviews written just before the app is uninstalled.

Can that be a reason for the account be banned?