My least favourite sharp edge of Mastodon is the fact that when you view someone else's post you only see replies to it that are known to your server - so there's actually a good chance there will be replies that are completely invisible to you, especially if you run your own instance
I'd love it if tapping a post kicked off a request back to the original server that fetched the current reply count and provided a "view all replies" button if there were replies not yet visible to me