I just had this happen to me. In my case the warning was given because of "mixed content" on my website. Mixed content simply means that there is an image being displayed on a page that is hard coded http:// instead of
https://. I had seven such images on two pages that were setup six years ago. Once corrected, the warning disappeared.
There is a free utility named
HTTPS Checker available for download that will find such links by crawling your entire site in just a few minutes.
Looking ahead, the next thing that will evidently be targeted in the same way will be the use of "www" in any link. It's all part of a major effort to eliminate exploits being used by bad actors.
Thanks for pointing out this issue Robert.