From 21st January every videos are taken down that are made for my website. Videos uploaded by me and the videos made/uploaded by users are taken down and showing reason flagged/spam. All videos are "how to ..." videos targeted to my niche. Is it Youtube or some one intentionally flagging them? Many videos had 50,000+ views and few months old. I am not following any method to promote the videos, just upload and natural views. What should I do? Thanks.