Your OS (Please state whether it's 32 or 64bit as well):
Windows 8 64 Bit

Your ISP and country:
Virgin Media - UK

Which zone you were in:
Typically Plaza 1, but it has happened in Regants

Were you sitting, standing or moving:
In Plaza 1, I would have been standing.
In Regants Legacy, I would have been moving, but regularly (5min interval) swapping between Boss Room and Main Regants Legacy

How long were you in the zone before you noticed chat stop working:
10 mins+

Which chat channel(s) stopped working:
All CUSTOM channels
Team
Direct

Local and Buddy chat DID function

Are you running full screen or window mode:
Full screen

What port number(s) you use:
Anywhere between 27000 and 32000

Multibox/dual logging users - do you use the same install or a separate install for each login:
One install. Change port configuration between logins.

Anything else you think may be relevant or irrelevant:
When this bug occurs, you can communicate in the channel, but cannot see other players responses in that channel.
Additionally, a symptom of this issue is that when accepting team invites, you will not join the Team.

It will be tricky for single boxers to even notice they have this issue, because for all intents and purposes, how can they tell that their chat partner(s) is simply not responding to them.

Additionally, I have had cases where one of my instances is not affected by the bug, and rest are.

The only way to correct the issue for me is to relog. Zoning does not fix the issue.