The SSL certificate for https://lists.koha-community.org/ is coming up as invalid as it has expired.
Created attachment 90401 [details] 1 - Error message in Google Chrome
Created attachment 90402 [details] 2 - Error message in Firefox
Created attachment 90403 [details] 3 - Certificate information in Google Chrome
Created attachment 90404 [details] 4 - Certificate details in Firefox
Looks like this is fixed and valid certificates are now in place.