YouTube has been starting to use AI-driven algorithms to try finding videos with potentially extremist or otherwise inappropriate content. Most of these get reverted within the first few hours/days but some just stay and don't run ads. The reason to this is because Advertisers didn't want their ads played on problematic/tragic/extremist content. If you have received enough Views within the last week though you may request a manual review to get the restriction lifted. This does not affect YouTube Red earnings, those will still come in on the video.