MongoDB Client Access Control: SCRAM-SHA-1 authentication failed, storedKey mismatch

As per the documentation, the object passed to createUser should contain a user property (along with the others):

db.createUser({ user : "admin", pwd : "admin", roles : ["root"] })
                ^^^^ not `createUser`

Probably you're trying to recreate the database with new login and/or password. So, you need to exclude the "/db" folder. The database path's in the docker-compose.yml file. e.g.: "volumes: - ./db:/data/db".