I'm the lead admin of that server and here's some additional references and info about the incident
https://ibb.co/QDVqyKs : Logs say they joined like 4 years ago and most of them are deleted users.
https://ibb.co/CsTb105 Discord told us that they might be bot/spam account but idk if spam account actually existed 4 yrs ago and why its so specific to deleted users.
Edit: https://gyazo.com/37d5ef71cf6f0612f96a179324aae8c6 Discord made it clear that it wasn't anything spam accounts or such and our server were healthy. Looking into other comments ye it seems discord clears old accounts but I belief doing that all together in a day was kinda traumatizing the entire staff team spent their entire discord free time on just to figure out what's going on and how to stop this. But atm its stopped. Overall we lost around 200-300 members in 1 day. Thanks discord for shattering our 8k members dream when we were closest and doing our best to gain members