HTTPS Injected into HTTP site?

We have been using your plugin for some time. Thanks! Anyhow, occasionally our site stops loading almost all images and I finally traced it to the fact that something was changing the http:// urls to https://. I contacted Themeco who makes our theme and they responded:

You have installed Autoptimize plugin and it seems that it serves the minified resources using https. Since you do not have an SSL, the plugin resulted to an error. We recommend that you disable this plugin and test your site again.

Is this possible? It kind of seems like this might have come up before you were installed on 1,000,000 sites… I checked the various settings and didn’t see anything involving http vs. https so I would be really surprised if your plugin changed this, but I just wanted to see if we may have misconfigured something that might cause this?

We have already fixed the html and the minified files are doing fine now, but they will eventually break, as they do every month or two even when we haven’t edited the site…

Thanks for any insight you might have!

The page I need help with: [log in to see the link]