I saw that yesterday on my phone too. Or at least I think I saw the same thing. If I tried to react to someone’s post, it would put the reaction on the previous post.
For transparency, we added the emoji reactions as a replacement for “agree” 
and “helpful” 
. It can be handy to react with a larger variety of emoji, but we aren’t entirely happy with the way they look on the site. So we are going to put some work into it in the new year. In the meantime, I’ll see if we can fix this bug. (And thank you for reporting it! I thought I was going crazy.)