There have been some occasional fails. Most are due to emergency services.
Here is a useful thread from 2 years ago that lists some successes and fails of SN.
https://sanctioned-suicide.net/threads/sn-successful-and-unsuccessful.30211/
Similar resource:
https://sanctioned-suicide.net/thre...nd-experiences-information-google-docs.29900/
There aren't any very up to date lists of SN attempts as far as I'm aware.