On July 8, 2023, user accounts on the Vivaldi Social Mastodon instance started disappearing. The incident began when the author noticed that their home timeline was empty after logging back in. They quickly reached out to colleagues who experienced the same issue. It was discovered that the affected accounts had been deleted and re-created as new accounts when users logged back in. The author and their team investigated the issue and discovered that all accounts with an ID lower than 142 were missing from the database. The deletions continued, and the team contacted Mastodon developers for help. Eventually, it was determined that the problem was caused by an account merge worker that merged all accounts with matching URIs into one remote account due to a timing issue with database replication. The team worked on recovery efforts and implemented patches to prevent future incidents.
https://thomasp.vivaldi.net/2023/07/28/what-happened-to-vivaldi-social/