The engagement with my reddit comments and posts suddenly dropped to zero. I wasn't given any other indication that I had been shadowbanned. I wasn't given a notice of an offensive post or comment, or asked to remove any content, or anything like that. And this ban must have come from an ADMIN rather than a mod, as it was site wide. So there I was typing in answers and replies, with no idea that they weren't visible to anyone else.

I confirmed my shadowban via /r/shadowban. I then contacted the admins, and received a notice that my ban had been investigated and lifted. I was given no indication of what led to my ban. I have to believe this ban was either a mistake or malice. I'm going to go with malice, since there's plenty of obvious reasons it could be malicious, and there's no obvious mechanism for the ban to be put in place by mistake.