I've been doing YouTube over the last eight years, and actively over the last two years and I have never experienced random demonetization. Earlier this year YouTube stopped monetizing videos on channels with less than 10 000 views, but the way I see it, that's a good thing as it makes it less profitable to make short lived channels which just steal content from others. I hope this in turn gives more revenue to those who actually create great content and aren't into it just for the money.