You might need to have the ‘show nfsw’ setting turned on. Anyway, they look like this:

So the theory that they were downvoted for spamming someone’s feed likely has validity.

I screenshotted this from their ‘trending’ page, which suggests that their content is garbage and their tech is fucked.

Hmmm. Speaking of Fediverse interoperability, platforms other than yours (Pandacap) typically arrange things so that https://pandacap.azurewebsites.net was the domain, and something like https://pandacap.azurewebsites.net/users/lizard-socks was the user, but Pandacap wants to use https://pandacap.azurewebsites.net for both. Combined with the fact that it doesn’t seem to support /.well-known/nodeinfo means that no other platform knows what software it’s running.

When your actor sends something out, it uses the id https://pandacap.azurewebsites.net/, but when something tries to look that up, it returns a “Person” with a subtly different id of https://pandacap.azurewebsites.net (no trailing slash). So there’s the potential to create the following:

1. https://pandacap.azurewebsites.net/ sends something out.
2. Instance hasn’t heard of that, so looks it up, and creates a new user in its database, with the returned ID (https://pandacap.azurewebsites.net)
3. https://pandacap.azurewebsites.net/ sends else something out. Instance looks in it’s DB, finds nothing, so looks it up and tries to create it again. The best case is that it meets a DB uniqueness constraint, because the ID it gets back from that lookup does actually exist (so it can use that, but it was a long way around to find it). The worst case - when there’s no DB uniqueness constraint -is that a ‘new’ user is created every time.
4. Repeat step 3 for every new thing you send.

If every new platform treats the Fediverse as a wheel that needs to be re-invented, then the whole project is doomed.

Firstly, sorry for any potential derailment. This is a comment about the Markdown used in your post (I wouldn’t normally mention it, but consider it fair game since this is a ‘Fediverse’ community).
The spec for lemmy’s spoiler format is colon-colon-colon-space-spoiler. If you miss out the space, then whilst other Lemmy instances can reconstitute the Markdown to see this post as intended, Lemmy itself doesn’t generate the correct HTML when sending it out over ActivityPub. This means that other Fediverse apps that just look at the HTML (e.g. Mastodon, KBIN) can’t render it properly.
Screenshot from kbin:

Also, if you add a horizontal rule without a blank line above it, Markdown generally interprets this as meaning that you want the text above it to be a heading. So anything that doesn’t have the full force of Lemmy’s Markdown processor that is currently trying to re-make the HTML from Markdown now has to deal with the ending triple colons having ‘h2’ tags around it.
Screenshot from piefed:

(apologies again for being off-topic)

Update: for LW, this behaviour stopped around about Friday 12th April. Not sure what changed, but at least the biggest instance isn’t doing it anymore.

I’ve since relented, and filed a bug

A bug report for software I don’t run, and so can’t reproduce would be closed anyway. I think ‘steps to reproduce’ is pretty much the first line in a bug report.

If I ran a server that used someone else’s software to allow users to download a file, and someone told me that every 2nd byte needed to be discarded, I like to think I’d investigate and contact the software vendors if required. I wouldn’t tell the user that it’s something they should be doing. I feel like I’m the user in this scenario.

I can’t re-produce anything, because I don’t run Lemmy on my server. It’s possible to infer that’s it’s related to the software (because LW didn’t do this when it was on 0.18.5). However, it’s not something that, for example, lemmy.ml does. An admin on LW matrix chat suggested that it’s likely a combination of instance configuration and software changes, but a bug report from me (who has no idea how LW is set up) wouldn’t be much use.

I’d gently suggest that, if LW admins think it’s a configuration problem, they should talk to other Lemmy admins, and if they think Lemmy itself plays a role, they should talk to the devs. I could be wrong, but this has been happening for a while now, and I don’t get the sense that anyone is talking to anyone about it.