Did a test yesterday with about 40-50 users on my forum simultaneously. It was during 90 football match were we replaced live forum with chat.
Given my team lost I got lots of critical feedback. It was a good cat to kick.
Discovered a few things.
Seemingly issues associated with number of users. Some people reported they were unable to log on, others got booted off. The same users had no issues later on. No errors messages were reported to the user.
Posters didn’t like being able to to use the emoticons on their own posts. They also didn’t like how posts got amalgamated, if they posted 2 or 3 times in succession. They would much prefer seperate posts.
A few struggled with being able to join to leave groups. This turned out to be more of a IT literacy issue. However clearer icon/ better description in drop down might help.
What people liked is the privacy on an otherwise open forum. The ability to replace a few WhatsApp groups.
Key things for them (given I explained it as forum = stuff you want to store vs chat = calling the referee a muppet) is ensuring chat is transient. Something like all chat older than 14 days is deleted. Or entire chat rooms self destruct after 14 days. This was part of the privacy side.
The ability to manually delete chat rooms would also be great 
They liked how posts moved to forum where linked back to the chat.
Hope feedback helps 