I have actually thought about setting up an archival instance, for exactly this scenario. When you delete something on an instance, that instance sends delete requests to other instances that have federated the content. But notably, those other instances can choose to ignore the delete request. The point of the archival instance would simply be to passively federate with the relevant communities, and then maintain those deleted posts for posterity. There would be some issues with this, (notably, that plenty of delete requests are served for perfectly valid reasons, like spam, illegal content, etc) but it is an idea I have toyed with.

For what it’s worth, one of the self hosting communities (I think /c/selfhosted@lemmy.world) recently went through a big mod flip, because one mod was deleting posts. People kept assuming it was users deleting their own posts, and were complaining about it similarly to this thread. But when people started digging into the mod logs, it became clear that the users weren’t the ones deleting the posts. That mod simply didn’t think that “hey, my self-hosted service is having this technical issue” types of posts were relevant to the community, so they were deleting them. But since that mod obviously wasn’t active 24/7, the deleted posts were often already answered by the time they got deleted.

It’s entirely possible that we’re in a similar situation here. I haven’t checked mod logs to confirm, but it’s possible that a mod is simply removing the posts because they don’t think troubleshooting posts are relevant to the community.