Only thing I could think if is that the work networking services could be impacting the connection or other networking users online at the same time doing something. Not sure what your work ISP would be and what or if they even have a modem or other means of providing Internet the the users.
I would try this, take the DSM home and test it out there and see if it exhibits the same thing If you have a host router and ISP modem setup at home. Even a friend or neighbors if you don't at home.