Your comments

Wouldn't the spam filter prevent the comment from appearing at all? The comment has always showed up in the comment section after hitting the submit button. It seems odd that a spam filter would crawl through existing comments and work retroactively.

As for a highly negative score, there are some pretty caustic comments on both sides of the ideological fence that don't get down-voted enough to disappear over the span of days, so it seems unlikely that something middle of the road, or not at all contentious, could be down-voted enough to disappear in just 5-6 minutes.

Going back to figure out which posts had a disappearance would be sketchy, but the next time I notice it happening to a fresh comment, I'll send you a link.
I think we may have a disconnect here on terminology.

Looking at each photo as a "post" with its own original "caption" (headline), and the "submit a caption" function as a "user comment", it's the comment, not the headline that is disappearing. I'm not doing anything with albums, just viewing photos by going to the gallery link and selecting "new" as the filter option, then viewing the photos and commenting every so often.

I do realize that some photos are re-posted frequently, but that is not the issue here. I'll go back to the same photo, in between the same two adjacent photos, with the same 3-4 other comments, and my comment that appeared when I first posted it will then be gone.

There's no rhyme or reason to which of my comments disappear, I seem to have about an 80% success rate with the comments staying there until down-voted enough to roll off the page. It doesn't seem like sending you a link to a post where a comment has disappeared would show much, unless there's a traffic log in the background somewhere.

Apart from that issue, I'm finding the general operation of the rating system sort of curious. I'll see a post with 15 +/- comments and ratings on some comments well into negative numbers, but then another post with only 4-5 comments, with comment ratings at zero and above, where it's clear from the existing comments, that other comments have been truncated. I did look for an FAQ that would explain how the ratings work, but didn't find any info.