Lessons learned
On mobile, I made sure the feature is working in the same way as on desktop. People usually read from left to right, a habit that started long before screens were invented. This is why I decided to show reactions from left to right, by timestamp, with the most recent one on the right.
Although the reading pattern argument wasn’t very strong in meetings with developers, I noticed the second one—`this is the standard used by Slack`—was better received. 😃