User Is being Disconnected

Hi,
I made an Ubuntu 18.04 server with the basic quick start installation.

On testing with a group of 3 users, one has low bandwidth and keeps being disconnected after about 10 seconds. I have told him to check with his ISP, but I want to be sure its not my configuration not allowing JVB to work on port 10000 udp ipv4. I seem to have it listening on ipv6 but not ipv4. Can someone please tell me how to easily check the problem is not caused by JVB not running on port 10000?
Thanks

Hi, I have just held a meeting with 3 others and all went OK so I assume JVB worked OK on udp port 10000 ipv4.
I do have a problem with frozen users and will ask on another post to keep it simple!