This normally happens due to inactivity at the workstation. That is activated by having system value QINACTITV set to a value other than *NONE and QINACTMSGQ set to *DSCJOB or to a message queue name. A message queue would have a program receiving the messages and choosing to issue the DSCJOB command.
A “disconnected” job is similar to a password-protected screensaver. The user should able to enter their profile and password and step back into the job where it was interrupted.