So if we start with the certificate presented to the visitor by Cloudflare, that one looks alright to me. Then your host appears to suggest that the certificate on your server is somehow invalid. I can’t check that, but depending on the encryption mode configured in the Cloudflare dashboard (SSL/TLS) traffic might very well be passed successfully despite the status of your own server certificate.
Moving on to WordPress, that is definitely not my area of expertise. But if the plugin somehow connects to your server directly (to update some WP content?), then an expired certificate on your server could be problematic. Maybe the next step would be to confirm that the certificate on your server actually has a problem. Are you somehow managing the certificate yourself or can you ask your host?
Edit to add: You might also ask yourself, is this error caused by my certificate? It’s not clear where this plugin is connecting.