Me and a friend were wondering about this the other day. We were stood next to each other and chat was available to me, but not for him.
We were wondering if it was because he was on ISA and me on Invest, so he switched to Invest momentarily. Still chat wasn’t available to him. We then thought maybe it was because I have a higher valued account and was a more active user so got priority?
We also tried logging in and out a few times but each time I got access to chat but he didn’t.
In the end I just guessed it was because he was connected to a different server and it was luck of the draw, but it does make me wonder if there are any variables to it being available such as some users have a higher priority than others rather than pot luck which server you are connected to?