I have seen this behavior multiple times on my website and several other websites where adsense is used.

The webpage is loaded fully (visually) i.e. all page content, adsense ads are fully loaded but the loading wheel in chrome browser keeps on rotating and I can see the message at the bottom-left of the browser "waiting for ad.doubleclick.net"

When I try to search why this happens, most users in various forums are suggesting to users (who are facing this behavior) to install a adblocker which will in a way block ads and will thus not see this problem. I think it is something which is unnecessarily encouraging people to install adblockers for totally unrelated reason.

Anyone knows why this happens? I am sure, I am not doing anything wrong with the adsense code. Anything, we can do to avoid it.