SSL mixed content on Pro Sites checkout

Hello.

Earlier this year, i got help from Thomas to make the HTTPS work on my site. (Link: https://premium.wpmudev.org/forums/topic/force-https-ssl-on-mainsite-and-http-on-subsites) Our site should only load HTTPS on the Pro Sites checkout page, and we got it all to work at the end. But after I switched theme, the problem is back. I have a messed up checkout page, because the page has mixed content loaded from HTPP and not HTTPS.

You have support access. Please help :disappointed: