A user reported that using AtCore Test Client with a Graber i3 with marlin, when printing a file and hit on Emergency Stop, the action worked, but all control of the printer was lost. Only restarting the printer and the host that the control returned.
For some machines this is the expected behavior. It will come down to how they have configured the "Kill Method" of the firmware. Some will reset the controller and some will just kill the heaters and wait forever o be restarted