Yesterday I noticed my OpenID URL stopped working on meta, SU and SF. I was already logged into SO and didn't want to risk being locked out of my account so I h. My OpenID provider is MyOpenID.com, which is delegated from my blog URL. Using the myopenid.com URL directly seems to work, but my account is associated with my blog URL, which doesn't work. I get the message
No OpenID endpoint found. However, it continues to work fine with other OpenID Relying Parties, as well as the various OpenID testers.
I actually had to create a new account just to report this bug. I suspect many users having the same problem aren't going through that trouble.
(Unfortunately my alternate OpenID was provided by Google using the profile-username URL format, which I recently switch to use userID format after the whole Buzz privacy debacle. I forgot to update my account here.)