Salrite posted...
I'm pretty positive Youtube does this sort of testing on certain selections of accounts.
Almost certainly. When they had that period of really trying to crack down a couple years ago, it was only ever a subset of people that had the site stop working for them until they waited for an update. It's not uncommon for social media in general to only push new features/changes to a subset of users at first so they can get feedback by comparing the experimental group to the control before rolling them out fully, and in the case of anti-adblock measures, that also delays the adblockers' responses because they've got fewer opportunities to collect data on what's being blocked.