The sub appeared to be working normally, I posted about the Amazon Redshift Serverless PDF, and then Reddit began behaving oddly.
After some investigation, and some guesswork, I concluded my account had been silently shadow-banned, and the sub banned (and then shortly after, deleted).
(Shadow-banning means when you log in as yourself, you see all your posts, and you see them in the threads where they were made. If you view Reddit when logged out, you then see all your posts have been deleted.)
Two years of posts and the sub disappeared, instantly, abruptly, without warning, reason, appeal process or notification, and Reddit is trying to lead me into thinking my account is still active. Make of that what you will.
Having had that experience, I concluded Reddit is not a safe place to invest time in.