Is this option enabled on this site?

If yes, there is a bug when using avatars from an external site without SSL.

Here's an example of a member avatar with http - This does not secure the connection when viewing All Activity on this site.

When I click that avatar image I'm redirected to the https version. Which user is using that avatar?

If file initially requested on HTTP, it causes "mixed content" issue and it does not matter whether it's redirected to https.

This user.

@bfarberAs @Mr 13 said, yes it is a member with such an avatar.

 If you view avatar info you will see a link http://....

Thanks (I didn't know where you got the link from, which is why I asked).