User unable to connect to conference rooms, but shows multiple instances of nickname

I have a user who is unable to connect any conference room, receiving an error message of “Unable to join room at this time: No response from server.”

In one of the conference rooms, other users see multiple copies of the errored user as ‘nickname’, ‘nickname 2’, ‘nickname 3’, ‘nickname 4’, and ‘nickname 5’. In another conference room, the errored user is seen as ‘nickname 3’ and there are no duplicates.

When I look at the admin console, the first room shows just one instance of the errored user as ‘nickname 5’ and the second room shows one instance as ‘nickname 3’.

Where can I look to find out what’s causing this issue?

This sounds like a configuration problem with the server’s xmpp domain name and what the client is using to connect to the server as. Please verify that you are using the most recent software releases of Openfire and whatever client you are using. Also, that the Openfire admin console does not report any DNS configuration issues on the main page.