A commercial came on 30 minutes into the 2nd cycle. This one is now off my list. And makes me leery to play any more from the channel, despite the good work. Sad & nearly infuriating.
I hate mid-roll ads as much as you do (possibly even more). YouTube has become VERY aggressive with their advertising settings. They now do it whether creators say YES or NO. (For the record I definitely say NO.) Sorry this happened to you!

We also need to understand that eight hour videos have huuuuuge files... and data transfer isn't free. Unless you're signed up for YouTube Premium, it will likely happen again.
A much less expensive option: I am currently offering this track for "pay what you want" pricing if you'd like to give it another try directly from your device with zero advertising. https://bit.ly/sleep-101
Darren Jurme