deleted the database

this is generally something you should avoid doing with activitypub software, as there is no clearly defined way to deal with changed private keys and it is handled differently depending on the software. with lemmy it should more or less resolve itself after some time, as instances will refresh public keys from time to time. after a few days of being alive again and having activities federate out it that part should start working properly again.

Subscription Pending Issue

check if your instance is considered dead, it may take sending some activities (e.g. subscribing, posting, commenting) and a bit of waiting to get your instance considered reachable again. you can use https://phiresky.github.io/lemmy-federation-state/site to check the instance you're expecting data from and look for where your instance is listed.

Old Content Persisting

as @asudox@lemmy.asudox.dev already mentioned, all you did was disappear. how would anyone know that your intention was to delete data?

while you can't force other instances to respect your deletion requests, it would still be possible to ask them for it, but this is not an easy task once they're no longer in your database. the most effective/efficient way to do this would probably to first get your overall federation fixed/not considered dead anymore, then delete the account using the same name, and never use the username again on the same domain in the future, as deletions are more pretty much irreversible and depending on the software on the other side may permanently block the username from being used, even if you change this in your database. another option could be creating posts/comments with matching ids in the database and then deleting them via api, but this is also rather fiddly and a lot easier to fuck things up with. i don't recommend editing the db directly without good understanding of lemmy's internals.

Old Replies Resurfacing

Lemmy uses numeric incremental ids for posts and comments, so when you started with a fresh database these ids are getting reused. this will break your posts and comments from properly federating to instances that have seen them with the same id before.

the easiest and lowest tech solution to deal with this would be to simply move to a different domain/subdomain for a proper new instance experience. alternatively you could consider adjusting the sequences in the database used for new post, comment and pm ids, to ensure that they are higher than any number your instance may have previously seen. as they are incremented not only by local content, but also by content retrieved via federation, these numbers will be significantly higher than the amount of content you had posted in the past, but it will be hit or miss whether they will overlap with ids that were for old local content.

based on counts from lemmy.ml and lemmy.world, it seems that a post sequence starting at 55m is likely safe to use, 20m for comments. pm ids are not publicly visible, but unless you sent or received many in the past, something like 1k or 10k are probably still safe bets. this is a db modification that you will need for sure if you want to minimize federation issues while using the same domain.

looking at your instance i'm not sure if this is what you mean by replies resurfacing, as i don't see any replies by remote users on your comments, but what i described is otherwise going to cause issues randomly in the future if you happen to hit a previously locally used id on a new local post/comment.