I went to the "learn more" link, read the article, and was not enlightened thereby. I added this comment to it: "This article was linked from my suspension notice by way of explanation of why my account has been suspended — but I didn't violate any of these rules, to the best of my knowledge, so the notice needs to be more specific."

I followed the "Learn more" link, read as carefully as I could... and remain unenlightened as to what the problem was. The key points — the "don't"s — seem to be these:

1. Don’t post concerns about moderation in the main newsfeed. Public conversations about moderation detract from the intended purpose of connecting neighbors on Nextdoor. They are almost always counterproductive.
2. Don’t engage in retaliatory reporting. Reporting messages because you’re upset with someone is unneighborly and violates the Community Guidelines.
3. Don’t attack, berate, belittle, insult, harass, threaten, troll, or swear at neighbors (whether they are members or Leads) who may have reported your content or voted to remove it.

Aside from the vague hint in the notice itself — "If you have concerns about community moderation, including why your content was reported or removed, do not post about it in the main newsfeed." — I have no idea why I've been suspended.

1. I did not talk about moderation on the main newsfeed; I talked about it in my Politics group, whose posts do not appear in the main newsfeed.
2. Pretty sure I wasn't doing this. I've been careful only to report posts and comments that are both clearly in violation of the spirit of ND's guidelines, as I understand it, and actually problematic in some significant way. If anything, I have erred on the side of underreporting.
3. I have indeed called other users out for being jerks or assholes, because I was under the impression that their misbehavior was not a reportable offense -- but I've not done this since suspension #2.

So I don't actually know what I was suspended for. I may have to try some tests.

If it is about discussing moderation in a public thread, though: users need to be able to talk about moderation openly, in order to prevent bullying and disinformation-spreading by people who know how to do it without breaking the rules... and ND needs to be clear about which venues are acceptable for discussion (the guidelines as I understand them only say not to discuss it on the main newsfeed, which I did not).

There have been similar problems with posts and comments (not just mine!) being removed -- there's never any explanation given at the time as to what the problem was. Sometimes emailing ND Support will evoke some information, but too often these inquiries are left unresponded.