Did you check with multiple browsers and devices (resolutions)?

Maybe have someone else take a look at the site. Fresh eyes.

This is likely a flag that follows a human review.

Also look for ad placements that can be confused for navigational elements.

You may not have changed anything to your layout but your layout is changing even if you don't realize it.

Updates to templates, CMS or plugins can break a template or plugin and cause it to do something unintentional. For example, to show how this happens, the underlying CMS might stop using a JS version and update to a newer version, causing issues with the template which relies on the older version.

So definitely review the site and look for layout changes, particularly mobile, that impact the ads, both in portrait mode and landscape mode.

And don't just look, but click through the site, using the different forms of navigation. As an example, there could be a navigational element that unintentionally drops over an ad.

Another way you can identify the problem is by looking at your stats in AdSense/Analytics, and looking to see if any specific pages, ad units, browser or geo-locations have unusual stats, like much higher than average click through rates, or potentially low coverage (in the case were Adsense has already taken action and stopped showing ads).

I also noticed that you posted another thread about a drop in Facebook traffic, if many of your users are coming from Facebook then they are likely viewing your website using Android-Webview "browser". Which isn't really a browser but a means to display your website from within the Facebook app. Others have had issues with AdSense and Webview.

If you have Analytics and Adsense linked you can generate a report that shows you CTR for Android Webview users, I would start there.

I do indeed have the majority of visitors coming from android webview.

Anyway, I noticed that my responsive ad units on mobile had a fixed width and height which were causing an overlap. I removed the height/width requirements and I see that the overlap is gone now. I hope that fixes the issue.