I'm not seeing this, however I may not be in your niche. The only comment I can give is that this is usually a temporary (but sometimes intermittent) issue and it affects many, not only with In-Article Ads but most other ad types as well.
We've had numerous discussions and most believe it is directly related to ad inventory, plain & simple.
What's puzzling is that it can sometimes be browser specific. No ads in one browser, come back with another browser and the ad is there. So maybe not everyone is missing the ads, and of course ads are usually geo specific.
@keyplyr, I am not blocking any ads at the present time. I'm allowing every category. It's very strange. No, the ads are not being served anywhere across 40,000 pages. Today I removed the in-article ad and replaced it with Conversant Media.
@levo - No, I didn't get any error messages in the console.
If Google's algorithm thinks your visitors are not having a valuable experience, you will lose enhanced text ads. Based on my experience across a number of client accounts, in-article ads seems to leverage the same rating system. For sites which were missing arrows, in-article would not fill. Once I fixed the enhanced text ads so they satisfied the algorithm, in-article starting working as well.
As an experiment, place a text-only responsive unit on your site. If arrows do not appear in the ads, then Adsense will not fill native ads either.