Use Ad Dropper with page caching

Many publisher sites cache whole pages to load faster. That usually means every visitor gets the same copy of a page, including the same ad, until the cache clears. Ads stop rotating, and a scheduled ad can keep showing after its end date. Ad Dropper 1.9 and later can load ads after the page loads to avoid this.

Turn on Load Ads After Page Load

Go to Ad Dropper > Settings.
Check Load Ads After Page Load.
Save the settings.

The cached page now holds an empty space for each ad, and the visitor's browser fills it in right after the page loads. Each visitor gets an ad picked for them: ads rotate, start and end on schedule, show the right desktop or mobile version, and are counted correctly.

It is off by default. Leave it off if your site doesn't use page caching, since ads then appear with the page and there is nothing to gain.

Stop the page jumping while ads load

Because the ad arrives a moment after the page, content below it can shift down. Reserve space for each zone so the page doesn't jump:

Go to Ad Dropper > Ad Zones and edit a zone.
Set Reserve Height to the height of the ads in that zone in pixels, for example 90 for a leaderboard or 250 for a medium rectangle.
Update the zone and repeat for your other zones.

If a zone holds both a desktop and a mobile ad of different heights, use the taller one.

Things to know

Shortcodes, the widget and ads inserted into content all work with this setting. You don't need to change how ads are placed.
Hiding ads from subscribers by level still works, because the ad is picked for the logged-in visitor.
If your caching or security plugin blocks admin-ajax.php for visitors, ads won't load. Most don't, but check this first if ad spaces stay empty.