Videos getting taken down

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.

Do you have external links in your videos? Misleading text, illegal downloads, some sort of repetetiveness?

Are they copied back to your channel?

not copied, yes link to the site in the description, not misleading, no downloads