According to this link: https://bf4db.com/player/ban/1916117133
my account was banned 4 months ago, but I was able to play normally until a few days ago. Is this a mistake?
No idea.
1. You've probably been playing on official servers.
2. Server Admin wasn't running BF4DB plugin.
3. Server Admin was running BF4DB plugin but decided to whitelist you.
4. Server Admin recently installed BF4DB plugin.
5. You joined a server that has BF4DB plugin.
6. BF4DB plugin.