Here are some important issues affecting the UX when chatting via a mobile browser:
  1. Flashing type cursor is missing. Users struggle to go back and edit text.
  2. Send, Emoji and Attach File buttons don't work after clicking into "Type a reply..." (greyed out)
  3. It's not obvious that the Return key is Send, especially if the Send button is greyed out.
  4. Occasionally "Type a reply" isn't clickable either.
Overall, these issues are almost a deal breaker for me. I sell UX services and it's not a good look when simple things aren't functional for new leads.
Issues were tested on iPhone X in Chrome. Will also test on Google Pixel.