Its almost certainly an anti spam system. The system marked the review as spam, for whatever reason. And it doesn't publish the results. The system doesn't tell

Its almost certainly an anti spam system. The system marked the review as spam, for whatever reason. And it doesn't publish the results. The system doesn't tell you this because otherwise the first thing you will do is keep trying again in different ways until it doesn't tell you it was marked as spam. Google drops reviews for a few known reasons. When a location gets negative coverage in the news, thousands of negative reviews from people who have never visited the location. Google then drops the reviews since review bombing is not useful. Who knows why OPs comment was flagged, but its easy to see how this happens without a big conspiracy going on.