ad tag imps vs actual pageviews

Hi all... any help would be greatly appreciated. I first posted this in the Programmer section, but that probably isn't the right spot. More related to actual marketing.

So, the situation:
This is happening to all ad tags, from 5 different networks - regular display tags (examples, medianet, criteo) and content widget tags (examples, revcontent, outbrain).

When a page loads that has an ad tag on it, it should record an impression to that ad tag id.For Display networks, even if not filled, it still does show an impression vs impression taken (fill rates). For Widget networks, it is always filled no matter what (as you get paid on cpc anyway).

So, if we have 100,000 pageviews, and we have a specific ad tag on that site, it should load 100% of the time right? It should record 100,000 impressions right? (give or take 5%).Well, for the past several weeks, this has not matched up for us. All our ad tags, are typically showing 40% less impressions then we are actually seeing in pageviews.

We have tried everything. Our site load time is fantastic, and we visual see the ads. However, nothing we have tried has fixed the issue. It basically is destroying our ROI and revenue for our site. The last thing we are trying is switching servers, hoping that it was a server issue - but in reality, is that a possible problem? This is our last resort.

Has anyone had this issue before? I'm sure it has happened to others. We are getting desperate. Any info or knowledge any one has would be much appreciated. Plugins, js code, php files, malware??? anything?

To note: We were fine before, and no discrepancies for the first few month of operating our website (ad tag imps vs actual pageviews were bang on or within 3%). It appears to start a couple months ago (with random days in a row at times being fine again). Since early June, it has been consistently above 35% lower ad imps to actual pageviews. We have made no changes during this time that should have this affect.

Thank you very much for any info that can provided.

 

Also I should note, we are not using an adserver and all ad tags/code is placed directly on site.