Weirdly, and annoyingly, I get this same thing when watching YouTube on my TV (the quantity thing, not the war propaganda stuff. Just regular ads). Whether via Roku stick, Chromecast or anything. It's sometimes an ad every 2 minutes. However watching the same thing on a laptop or my phone even without any adblock and the video will play far better. Maybe 1 ad at the halfway point and nothing else.
I don't know why the TV version of YouTube is such an arse for ads. They're not even in clean places - I get an ad mid-sentence.
Honestly, for a 20 minute video I'd be perfectly ok with a 30 second ad or so. It helps the creators and isn't that much of a pain for me. But getting adverts every 2 minutes, even if they're skippable is just a horrific experience.