Whenever I try to reply anywhere but at the first level, I get error message shown below, and unlike the report from another forumite, the posts do not go through, not in any kind of reasonable time anyway (a couple of minutes, literally). I have no trouble replying to the original, thread-starting post, and it happens even when replies are only nested 1 or 2 levels.
The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request post /posts/reply/1713961.
Reason: Error reading from remote server