@JLNobody,
Can't tell for sure, JLNobody, but you probably clicked on 'back' to see the thread (but you really just have to wait for it to show up once you click "reply"), and since you clicked on "back", you need to click "refresh" to see the new post. "refresh" is the curly arrow up at the top of the safari browser (on mine, it's the second thing on the browser line).