TV stations used to do this in the late 90s and early 2000s (maybe they still do it, idk) to increase ad space given the fixed time formats of the medium. Hulu doesn’t really need to do that, they can just make the ad breaks longer.

they could be doing it, it could be for nefarious reasons like making longer ad breaks seem perceptually shorter, it could be something stupid like they’re use the masters that were destructively edited by the above process (see 90s cartoons like ren and stimpy, Rockos modern life, Beavis and butthead, etc that retain censorship to this day because the original masters no longer exist unmolested), or (imo most likely) it could just be a technical issue. Most/all streaming networks have totally garbage apps and it wouldn’t shock me at all if their player introduced issues that fucked with timing at the expense of draconian drm or just bad lowest bidder coding. Of course, it could also be a problem with your setup

Easiest way to resolve these issues is piracy. You already have a plex server, nice. I recommend jellyfin to anyone starting out. Plex is fine but they ~~have~~ reserve the right to snitch on users in certain situations so fuck plex. If media companies stop being greedy and splitting catalogs all over the place then maybe reconsider. The music industry figured out how to have multiple vendors that all have 95+% of each others catalog, movies and tv can do the same. They’ve even gotten to the point where the apps are as good or better than my pirated library. My flac library is imperceptibly different from apple lossless, they have lyrics ready to go for the overwhelming majority of tracks and most are time synced (which I can’t be bothered to do for a 2tb music library, automated lrc downloaders are often wrong in my experience), their app has great ui, and with recent updates I can even remove vocals from literally any song. I’ll happily pay $120 a year to not bother with maintaining a ratio on red or dealing with mislabeled shit on soulseek