WordPress serving the old certificate still

Hi there,

I’ve been using this plugin for a while now and so far, everything has worked flawlessly. I got an SSL certificate from my webhoster and it seemed to work out-of-the-box. Now, after 12 months the certificate has expired and seems to have been replaced with a new one automatically (I can see the new one in the hoster’s web interface). But for some reason, wordpress still serves the expired one to the users, which causes the browser to reject it.
What am I missing? What do I need to do in order for it to use the new certificate for my domain?

Thank you very much

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