There’s currently an issue that causes a lot of communication between instances to be dropped due to expired timestamps: https://github.com/LemmyNet/activitypub-federation-rust/issues/46
It’s already been fixed in the code, but I don’t know when the new version will be implemented in Lemmy.
Not sure, but it looks like you’re posting to the wrong sub. Try !lemmy_support@lemmy.ml instead (see rules 1 and 3 in the side bar)