Still doesn't completely add up to me.

Who would even produce a 1- or 10- or even 90-hours long ad? Like, what advertiser would put that into the exchange? What would be their expectations?

Seems more likely to me YouTube is playing tricks here and just playing regular ads on repeat. Or selecting random other regular videos and playing them as ads, or something.

In those cases, it would at least be a clear case of punishment against ad-blocking users and not a "malfunction".

(I assume that no one went through the trouble of actually leaving the video on for 90 hours. So unless someone captured the video file, we have no idea if the displayed duration is actually correct)