I've tried to write with my friend on chat during an offline match but we haven't been able to read anything: the chat was blank.
Does the chat function only during online combat sessions?
As far as I can tell it only works for live games. The game log doesn't save the chat information. Even in a live game, if you leave and come back in all the chat lines will be gone.
This is correct; chat logs are not currently saved to the database and so won't appear during offline matches. This is something I'm considering adding for future release.
Thanks. It would be a great add-on :)