Hi Michael,
I can't see the attached screenshot, could you please try re-attaching it?
Are there any other users besides your co-worker that are accessing the same host system that do not encounter the issue? Do these random characters appear while navigating between the host screens or while they are inputting text? I'm assuming that they using VT Display, if so, could you please ask your co-worker to verify that they have configured the session to use the correct Terminal type found under Session -> Configure -> Edit -> Emulation? By default, VT Display is configured for VT320.