What do you mean? You should be able to reply and upvote both comments and posts. Which one are you having issues with? If there's an issue I'll take a look.

Edit: This might actually be a UX failure. Did you know you could swipe from left to right for upvotes and downvotes, then from right to left to comment? I know some people don't like this (or even know about it) so I'm going to add a toggle for this feature. During user onboarding (coming up here in the future) I'll have a screen that asks you to set a few basic user preferences (enable NSFW content, appearance, push notifications)