You have enabled your SSL flexible certificate on cloudflare.
What I did next was visited my site at the HTTPS location and start to look via the inspector at what was being delivered via HTTP
I went into my Xenforo control panel and changed the basic board configuration to HTTPS
I reloaded my site ( ensure that cloudflare isnt caching anything - I put mine into development mode )
I then used the inspector in chrome to work out what was being served in HTTP - things like where I had added icons / images to notices , or small node icons - I changed them with the template editor and got rid of them that way. Took a little time but now I have a green secure bar at TurboRenault.co.uk