It's probably because of the CSAM attack. They had to delete all images that were from that time interval. They also had to disable uploading images until they fixed the problem.
I see all of your images on top all time. Lemmy.world might be having some connectivity issues at the moment.
I love how 196 is an appropriate place for this question lol. I'm sure you have a reason.
As some said the CSAM attack was like... 6 weeks ago, I think? Everything older than that was deleted on many if not all instances. You can check how each instance dealt with it in communities such as Announcements, Meta, Instances. Of course a good keyword for the search would be "CSAM".
I'm going to guess that there's some kind of pruning going on just by virtue of the size of them. My Mastodon instance which is pretty well unused other than the few dozen people I followed on there has an image store or around 300 GB last I looked. Lemmy seems just as hungry though I've ran it for less time. Scaling that up to the biggest instance around and I'm sure they're at many multi TBs of storage just for things to chill there. Those on outside instances might have cached copies that the home doesn't though.
Be sure to follow the rule before you head out.
Rule: You must post before you leave.