It's Reddit's filters. They've had a huge update in the past couple of months. From what I can see, the auto mod for the subreddit bans posts if the user posting it has an account history of promo comments, low quality score, new account, broke subreddit's rules etc. If that gets missed then Reddit's own filters act as a second layer and delete the comment for the same reasons.
It's a black box, now they're using AI to moderate the site, it's extremely difficult to beat because that AI has been trained on hundreds of millions of promo posts, spam posts, bot posts, dodgy account behaviour and so on. Unless you were set up well before these new filters came into place, it's nigh on impossible now to get promo posts to stick, and I think, even if you were set up before these filter updates it's only a matter of time before you're caught up in the net as well in future updates.
