HTTPS requests to your apex name are fine but notice the error is for your www subdomain.
HTTPS requests to that name are using one of the most unusual sets of certs I have ever seen. Again, see the SSL Checker site. You'll need to review your WordPress or other config to see why this is.
Note that the first cert is for a name www.stackssl.com and which expired almost 7 years ago! Do you know what stackssl is?
Also, since you are using a www subdomain the good cert you got from my post #2 needs to be replaced with a cert with both of your domain names (the apex and the www)
Looks like your hosting provider is CloudNext. This issue was also reported more than half a year ago at Expired SSL | WordPress.org Seems that poster managed to get it fixed by talking to the hosting provider.
Weird thing is: the hosting provider still hasn't removed the expired www.stackssl.com certificate.