The "CYT" series invites you to analyze an RC flight problem. After a bit, the answer, and correct analysis is posted.
In this case, the pilot started having trouble controlling the quadcopter immediately after takeoff. I will give you a hint that the problem was NOT mechanical in nature (e.g. slipping prop, failing gyro, etc...). As a bonus reward for reading the video description, I'll tell you that the copter had just been upgraded from Betaflight 2.9 to 3.0.