Youtube is currently enforcing their ~~new~~ (edit: since 2019) guideline that prohibits any videos about “malicious or harmful activity” including hacking, especially hacking tutorials and (unintentionally?) anything related to Anonymous, even Interviews. This policy also extends to videos released *before* the guidelines change. Additionally the striking frequency is not calculated by the date of publishing but by the date of reporting. Due to the lack of support by YouTube by any means, some YouTuber delete their videos related to that topic to prevent their account to be deleted without pre-warning (due to several strikes in a row).
So if you have any favorite YT channel that published such videos at any given time, now is the time to download/archive all of them.
Edit: To prevent circular source references: I got onto the topic by the cases of the channels SemperVideo ([Link to their German Tweet about their strikes](https://mobile.twitter.com/SemperVideo/status/1334840519088893954)) and [TheMorpheusTutorials (German video)](https://youtube.com/watch?v=Xod64GBUnGs). They are German and therefore relatively small channels with poor support contacts from YouTube. But even if these strikes aren’t justified and get reverted after a community outrage—like in the [case of *Null Byte* in 2019](https://www.zdnet.com/article/youtube-ban-on-instructional-hacking-causes-infosec-community-outrage/)—the fear of losing the channel might get YouTuber without good YT support connections into proactively remove “dangerous” content like TheMorpheusTutorials did, who deleted more than 100 videos. I haven’t found much substantial secondary sources to that topic so take my information with a grain of salt.