There have been 291 replies from only 122 unique users; and 666 (how ominous!) likes given out.
Y’all are quickly achieving echo-chamber levels of commiseration! It’s only been a day, don’t peak prematurely.

And since we’re all friends here and just throwing out WAGs as to what happened, and why, I’ll throw my hat in the ring. Here we go…
Plex did their level best to positively identify those reprobates who violating their terms of service. Being the privacy-oriented folk they are, they weren’t comfortable with the idea of violating their users’ trust by digging through their private data; heck, they likely don’t even have the information to do so.
So, being that something they were able to positively identify is that a large number of these ToS disregarders utilized Hetzner’s platform for their illicit activity. Having determined that, they reached out to the good folks at Hetzner for additional help in narrowing down the suspect list. However, realizing that a good chunk of their monthly income was derived from these users, Hetzner declined to assist in any meaningful way.
Plex pleaded with them, letting them know that they (Plex) had to do something, as it was not good for their nicer, ToS-observing users; however, Hetzner steadfastly refused citing consumer protection laws and other equally convincing “reasons” for not assisting Plex in this endeavor. Finally, Plex had to act, resulting in the notifications received over the past twenty-four hours.
As much as it hurt Plex to do it, they knew that the only way to effect the required change was to take this step, hoping that it would finally convince Hetzner to act in their own self-interest. Plex knew that it would upset a portion of their user base, but were confident that positive change would result.
As I type this, there are multiple Plex decision-makers sitting in dark rooms with a drink in one hand and their head in the other, pained by the decision they were forced to make on their users’ behalf; wondering if, ultimately they had made the right decision. Only time will tell.
Of course, I don’t know any more than the rest of you do. But I feel the events outlined above are just as likely to have occurred, or be occurring, as some of the conspiracy theory-level of stuff I’ve seen in some of the comments above.
And I wish you all luck in obtaining refunds or some legal remedy for the harms that have resulted from this. There isn’t an attorney in the world who’d take on such a weak case. I’m not going to back that up with any sort of citing of law or legal precedent. Just go search for it on the Web; I’m sure you’ll find something. Or not, But that seems to be the order of the day.
And lest my snarky-ness above be perceived as having any amount of malevolence behind it, there is not. I feel bad for y’all. It’s never fun to get caught up in a “this is why we can’t have nice things” moment. But alas, here you are. I trust it will work out to everyone’s advantage, in the end. Except Hetzner’s, of course.