I was having the issue occur before on production and dev, but the repo I linked only has it occuring on dev, which of course would be much less of a worry, and is possibly a vite problem if it's dev only.

Edit: I can get this error in production to occur via my fuzz testing, I'm just having issue isolating the test to get it to occur cleanly in the sample repo

Affected LibUV Source seems to be a UTF-8 to UTF-16 conversion issue

With openapi-fuzzer installed you can kill a production remix.js server which has no routes defined. I still haven't pin-pointed the exact offending request yet, but the setup in the source will hit it eventually.

npm run build & npm run start
npm run fuzz:all

Since it is a libuv utf8 -> utf16 issue, I doubt it something directly in the remix.js code, however it does affect all remix.js express servers so I will keep this issue open until I can find the closest NodeJS dependency to this issue.
It possibly might also affect not express.js remix servers, though I haven't tested that yet.

Found an exact packet that will consistently kill a production remix.js express.js server
source

Note if you stringify the buffer then send the string instead of the raw buffer the server will not die.
It is very specific to a certain byte encoding

Edit: It seems to be a combination of the URL path + API-KEY header in that packet that creates the issue, because if you reduce the path to something that makes sense the bug goes away, but if you restore it and also remove that header it also resolves the issue, so it's clearly a conjunction of the two creating this issue

Removing these lines stops the issue from occuring:

app.use(
  viteDevServer
    ? viteDevServer.middlewares
    : express.static("build/client")
);

However leaving app.use(morgan("tiny")); does not affect it which implies it's not express.js, and instead is an issue present in viteDevServer.middlewares and what ever express.static generates, though I don't know what express does here.

I tracked down the offending cause, and confirmed by removing this call it does fix one fuzz test case, however I believe this issue should remain open until a patch is available because it doesn't explain how the other http headers were affecting this, and there is likely another issue also occuring, but is hard to find while there isn't a patch for this case.

remix.js -> express.js -> serve-static -> send.SendStream.sendFile:L629-L634

fs.stat(p, function (err, stat) {
  if (err) return next(err)
  if (stat.isDirectory()) return next()
  self.emit('file', p, stat)
  self.send(p, stat)
})

See nodejs/node/issues#55914

NVM, actually the API-KEY header might have been a red-herring.
It's up to the maintainers whether or not this issue should remain open as it's not an issue directly with remix.js, but does affect it quite spectacularly until patched.