Yannick
I was curious and tried it.
I can confirmed it in Version 0.99.132.1.2-rc (WebKit 621.1.2.111.4) safe mode.
For desktop browser, the problem of reproducing is YT is placing ad randomly in videos. It is putting much less at the beginning, but more in the middle and even at the end.
Additionally, I think YT is putting a time gap between ads, even across videos. Also it may not even show ad if you are watching a video the 2nd time.
I got lucky in the following recording. The ads were at the beginning of the YT video. Orion was in safe mode.
The YT video I clicked: