I guess that the recent changes messed with the certificate for the attachment server. And since there isn't a tons of complaint, it come from your computer, that have the wrong value for the certificate, or something like that.
Try to clean the cache of your web browser. If it don't solve the problem, try to reset the SSL state at OS level.
Note: In both case "how to do this" depend of your browser/OS, so google (or any other search engine) is your friend for the answer.