On a mac, there is this clever tool to turn off (parts of) applications that the computer thinks you are not using. This tool is called ‘app nap’.
For jamaseis, this has to be turned off. The following video shows how:
(Note: The initial part of the video shows how you can access the relevant settings by right clicking. You may need to hold down the control key on the keyboard while clicking to get to the contextual menus).