Quite hard to replicate, but I've now spotted this happen twice and think this is a bug.
Occasionally, Orion does not send form contents in a POST request. The webserver doesn't receive any contents in a request (I've yet to clarify whether it's still actually sending a POST request at all).
So far, I've seen this happen:
In a form submitted by JavaScript. Inspect Elements appears to show a POST request leaving the browser, but the server cannot see any contents of the $_POST variable
In a simpler HTML form. That form simply contained two hidden INPUTs, and was a standard simple HTML form. Hitting the submit button appears to have not send the contents of the POST.
This is the woolliest and worst bug report I've ever written; but my plan is to keep this updated as I learn more about this bug.
(Details as above, but I'll flesh this out later where I can)
Version 0.99.126.4.1-beta (WebKit 618.1.2)
Sonoma (14)