You said this also happens on different machines for the same user? Any of those machines running a different version of Mac, or Windows?
No, both of his machines are Macs and both are running Sierra.
You say: "I have logged in as that user from our office so an entirely different LAN and ISP was used, and the problem was duplicated"
Do you mean if you log in using his account the crash happens on your machine? If so, perhaps there is an issue with his account. Try setting up a fresh account for him and see if the problem persists.