In the beginning of this year, Google AdSense announced a new feature named Ad Balance that lets you controls help you reduce the number of ads you show to users, specifically the ads that earn you the least revenue, and see how it affects your earnings. This is all done via an easy to use slider in the AdSense publisher portal.
Well, sometimes, using this feature would result in unfilled ad slots that loaded blank space. Google updated their post to add that they are now going to be automatically collapsing any ad units that go unfilled.
Google wrote:
May 8, 2017 Update: We've heard your feedback on the empty spaces resulting from an unfilled ad unit. Over the next few weeks, we’ll begin to automatically collapse unfilled ad units -- if it's safe to do so without affecting the look and feel of your site. By using “Ad balance” you’re automatically opted-in to this update.Thank you for providing feedback to help us improve this and other AdSense features!
So if that was one of your pet peeves about this feature, you can not give it a try again.
Forum discussion at WebmasterWorld.