In the meantime, just don't be put off by the server error message. Just ignore it and refresh. Whatever you just tried to do (reply to a post, start a thread, like a post) probably worked. Before you try to do it again check if it worked the first time round.
What is causing the multiple posts is people doing things multiple times.
Edit: Just got the error message posting this using Edge on Windows. Ignored the error, refreshed, and there was my post.