This article is slightly different from my usual articles, as it’s more about the use of a chat client. However this issue has been one that has been causing me great pain and frustration, and having found the root cause of the issue has been quite a relief. I figured I would share in case others were experiencing.
Over the last 3 months, a group of friends and I have been using Google Hangouts as the primary medium for messaging. Due to the use of an XMPP Bridge, we are able to use chat clients like Digsby, Adium and Pidgin. This worked great, until one day I noticed one of my friends did not appear online any more, though I would receive messages from him. Attempts to remove and re-add the contact, as well as completely & mutually removing our Google Plus and Gmail Contact info from each other did not resolve the issue.
After 3 months, the issue and resolution was finally found on the Google Product Forums. It would appear that when you disable sound notifications in google hangouts for messages, unexpected behaviour can occur including that you will appear invisible to other chat clients. My friend verified this by un-muting notifications, and *boom* he appeared online in a variety of clients we were testing.
So there you have it, if you are having trouble with friends who use Hangouts appearing offline in your chat clients, see if they have muted/disabled message notifications.