Mixed content plugin Flow-Flow

Hello, I spotted a Mixed content problem on a page of one of my sites. https://christec.net/veille-technologique/

image : https://www.casimages.com/i/200806073011359862.jpg.html

When I use the plugin Flow-Flow with the MASONRY layout I have a Mixed content error message on this svg image. https://christec.net/wp-content/plugins/flow-flow/assets/oval.svg

image : https://www.casimages.com/i/200806073011481417.jpg.html

I correctly enabled FORCE HTTPS FOR ALL RESOURCES in the plugin but it doesn’t change anything, and SSL Insecure Content Fixer doesn’t fix the problem. Can you tell me how to fix this error.

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