Something interesting that has been happening to me in Brave for I guess the last couple of months (with the preface that I never see ads when I click on a video in brave):
In the morning, I usually go to my youtube main page and browse for any interesting recommendations. I generally end up picking 4-5 videos that I open in new tabs to watch later in the day. When I go to them later in the day, they run for like the first five seconds, then they reload and now have an ad for me to sit through. However, if I then immediately reload the page again, I'm back to ad free.