Someone private messaged me. I responded that same day with a page-long response. That message didn't go through.
So, I tried it again a few days later when I noticed that my response was gone. I spent another hour or so writing a response and guess what? That disappeared too! After I clicked "Message" to send my response, the messaging interface said something like "saving..." and a wheel spinning. But, it kept spinning and spinning and spinning. I don't know what happened afterward because I forgot about it. I must have closed the web page by accident.
Just to let you know, the messaging system doesn't like me and it's messing with my mind.
We send and receive a lot of private messages without any issues so far. What you describe could happen if there was a network issue or server restart at the same time, perhaps. Or if there was something about the message you were sending (e.g. length).
We do not write the forum software, so we can only make guesses about what kind of issue you may have run into. You could try https://meta.discourse.org/ but they'd need more information on how to reproduce what you're seeing.
This is why on all forms I fill out, before hitting send, I'll copy it to clipboard. That way if it fails, I don't have to retype it. Or, type it in notepad first and paste into the form.
I think I might have a clue. I think but not sure that when it takes such a long time to write a response, the status of the page changes. As a result, when you click Send or Reply, it won't accept it and it'll just keep saying Saving and not do anything.