Hi,

simple answer: Federation.

Federation takes time and if another instance didnt recieved the deletion users can still reply, vote and report it.

Deleting posts or comments is a best effort attempt at removing it from public view.

Due to the federated nature of Lemmy, any time content is posted and sent to other instances, we lose control over what happens next. When content is marked as deleted on our end, this sends a “please delete this” message to other instances, but there is no way to enforce this, as that content is no longer stored on our infrastructure. Once content is publicly accessible on the internet, there is no way to ensure that it gets removed again. Even if all fediverse instances are cooperating and honoring deletion requests, there may be federation issues causing the deletion request being lost, or external actors that just scrape Lemmy or the larger internet to collect as much data as they can, with no chance of the original creator being able to get it purged. Depending on the data, this may no be legal in some jurisdictions, such as EU having the “right to be forgotten” and similar laws.

Additionally, the Lemmy version we are currently using has a bug, where under some circumstances contents of deleted and removed comments are still being displayed to users. While this is expected for mod-removed comments to be visible in the modlog, this is neither expected for deleted comments nor should the comments still be displayed normally. We are looking forward to address this with the next Lemmy update we will be deploying, but we will likely have to build some custom patch for Lemmy to ensure that this does not significantly reduce our moderation experience, as the solution implemented in Lemmy essentially prevents anyone, including site admins and community moderators from seeing removed and deleted comments entirely.

This is further extended by Lemmy having a scheduled task (already in the version we are using here), which runs daily to overwrite deleted posts and comments to remove their contents once they are older than 30 days.

As is right now, if you have sensitive information that you accidentally shared in a comment or post, we recommend editing the contents prior to deletion and removing that.

edit: typo

Some instances just don’t comply with delete requests. Besides that, it takes time to federate, both directions, the comments could be from before you deleted it but took time to federate to you, or the delete request didn’t federate to their instance in time.