If you go to your own YouTube account to subdirectory “features” you can see if you have any Copyright Strikes or Community Guidelines Strikes.
The link for Copyright Strikes is here. A strike is called when a video is removed after a complaint from a copyright owner that the video violates an existing copyright, and has been removed under Digital Millennium Copyright Safe Harbor.
Merely deleting an offending video does not remove the strike (as it has already been removed). But the user can challenge the claim (under Fair Use) or sometimes get the owner to retract the claim if the user agrees to keep it removed (under the table). It appears that a strike remains active for90 days, and removal requires going to “Copyright school”.
A user who accumulates three strikes at one time has his or her account removed and all videos removed (including non-infringing and unrelated videos) and appears permanently banned. That could be a weakness: a litigious or “authoritarian” copyright owner could try to silence someone this way.
It’s common to see embedded videos disappear because owner’s accounts have been terminated for "multiple copyright complaints", usually under three strikes. But the disappearance of an embedded video created by someone else does not constitute a strike. Many infringing videos appear to be illegal copies of films or television episodes (sometimes of musical performances). My experience is that most QA sessions don't object to recording and posting. Most plays and (classical) concerts prohibit recording and would submit claims if posted. I'm not sure what happens with music recorded at rock concerts or in (DJ-serviced) discos (unless the venue has explicitly prohibited recording, but in my own experience most bars don't). Rebroadcast of sports events is usually prohibited but I haven't seen MLB prohibit incidental video excerpts of baseball games or of pre-game shows by fans actually at the games. (MLB offers its own embeds of critical game plays, which bloggers can use as free.)
Someone who wants a “future” or “career” creating his or her own videos should be careful about allowing copyright strikes.
Wikipedia has an explanation here.
A related idea is a “Content ID Claim", which seems more complicated and which does not by itself create a strike, link.
“Community Guidelines Strikes” follow a similar idea (link ). But in some cases, takedowns (as related to safety of someone or to unusual law enforcement concerns) don’t result in strikes. The recent controversy over Facebook Live could result in more pressure on YouTube regarding these “Strikes”.