Why does CHANNELS have a pencil and PERSONAL CHAT have a plus sign?
It was frustratingly non-obvious to me that the pencil sign was to join (or leave or preview) chats
It would be good if there were a back button or some navigation from this page. Swipe left is easy enough to guess but only just.
It would be good if there a join icon on this page instead of having to type a message - possibly unwelcome nonsense 
- to join the chat
The blue link on this page leads to an "Oops! That page doesn’t exist or is private." message
The back button here goes to the Channels/Personal chat page instead of the Preview/Join/Leave that I came from
I think the emoji selector needs one extra character to be typed after the colon (compared with the forum).