ActivityPub (the model that the fediverse uses for federation) is publishing-based, as the name implies. Like email, you’re sending messages to a list of recipients. Usually that’s your followers, people you mention, and the person you’re replying to.
If the recipient list is empty, then your message won’t leave your instance.

Threadiverse users don’t really have to worry about this too much because communities act as relays, sending your posts to all of the community’s followers as well. But microblogging instances don’t have that luxury. If they don’t have any followers, aren’t writing a reply, and don’t mention anyone… their post isn’t federated anywhere.

It’s also worth considering that only public data is federated. For example I wouldn’t be able to recover my bookmarks from another instance, and it doesn’t seem like Lemmy federates your list of subscriptions. Your posts may still exist elsewhere even when your instance goes down, but that’s not necessarily the data people want to be able to recover.

This is the fediverse, where many different software intersect. You should expect the possibility of incompatibilities with users from instances other than your own. When a post looks like something is missing, always open it on its origin instance before complaining. It’s likely your own instance is at fault for the issue, not the author.

In this case it looks like Piefed deleted the post’s title.

[Edit: PieFed did not show the title including the link to Reddit where additional information was provided.]

It reads like an instance by the name of MedMastodon went down with little to no notice.

Although this announcement seems to have been made on a Friendica instance that also isn’t cooperating (edit: hashtags) - certainly not to anyone without a login on that specific instance, which I imagine will affect roughly 100.00000% of all people reading this (and high ironically - in the Alanis Morissette sense - roughly also 100.00000% of the people that do not read this:-).

To anyone on Lemmy and wondering, there are additional hashtags that render on PieFed but not Lemmy, though it doesn’t help here since this is the only place that hashtag has ever been used (that PieFed here shows).

Oh, and the instance actually does return an error page saying “This instance is under maintenance.”, so it’s remotely possible that this Friendica message is based on misinformation, and that the instance being “down” may be only temporary? (I have no idea)

Some additional info I could scrounge:

Article about Med-Mastodon, basically saying to use both the X and then treat that Mastodon as a way to hedge your bets against Twitter enshittifying.

Hrm, it looks like their GoFundMe may have just run out, having started on Nov. 15, 2022 and lasting for 3 years? (I have no idea if there were any follow-up ones)

And at this point I’ve already put far more work into this than OP, it would seem, trying to guess what they meant, so I’ll stop here.🙄 (edit: this was due to a PieFed rendering bug)