If they had enough time to warn people ahead of time, they had plenty of time to push a fix to their system for this. We are literally talking about adding support for one more image format.
Emails, tweets, texts are no excuse for broken products. The iPhone is the best selling model in the United States. It is on College Board to support its default image format.
Good product design is owning your users' success. It is not sending people workaround emails.
The bare minimum would have to be to do a warning before every single AP test about this and giving students a few minutes to change their default image format. Sending a tweet (!!!) out does not count as doing any work.
This is a failure. An abysmal failure.