I'm trying to reply to a comment on my local wiki and I get the following error
Could not find the comment you're replying to on the page. It might have been deleted or moved to another page. Please reload the page and try again.
I think the culprit might be CommentUtils::getTitleFromUrl failing to generate a title and making CommentParser::findSignature return null.
URL: "./index.php%3Ftitle=User_talk:Admin"
See image for variable dump with xdebug
I setup short url and it works fine. Maybe $wgArticlePath ?