This issue has now been resolved. Facebook shares are behaving as normal now.
Feb 15, 03:53 PST
Our engineers have made a change to how we serve social share images to Facebook, which should resolve this issue. New shares of NationBuilder pages should render with the appropriate social share image moving forward. Our engineers are continuing to monitor this fix for any issues.
Feb 14, 10:24 PST
Our engineers have determined that the issue with social share images is originating from a recently discovered bug with Facebook. We're working with Facebook to identify and resolve the issue. We will update our status page as soon as we learn more.
Feb 11, 11:02 PST
We have had reports that new social share images hosted with Cloudfront are generating errors when creating social share graphic info via Facebook's Debugger.
Feb 10, 17:49 PST