A few days ago there where 100 bots called lucky who joined my game. I restarted the app again and again but they kept on having more! Overall a great App but please make the upgrades and the changes in the server. Please take my advice seriously and change it as soon as the company can.
What you described happens when player or players are sharing the PIN to the game externally or someone is using BOT services available online. Please contact us via kahoot.com/request and our support team would be happy to troubleshoot this with you.