I've never seen or heard of anyone having their activity level reduced.
Are you sure you're not confusing activity with posts? They are different. And post count can be reduced when threads that you posted on get archived or deleted. Some times individual posts can be deleted if there are complaints or the moderators deem it necessary.
Please give us more detail.
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I see.
I have 84 post, as well as 84 activities.
Probably some of the threads where i posted or commented were deleted therefore the number of my post were also reduced and my activities as well.
Thanks for helping me understand it better.