If the shift has multiple participants linked, clicking the GOMS session button should open separate tabs in your internet browser.
Each tab is a separate GOMS session for each participant.
If you are finding that only 1 tab is being opened, then this may be caused by the pop-up blocker on the Chrome browser.
If this is done on Safari on iPhone, it is blocked. Apple does not allow for multiple tabs to be opened. In this case one will open and then you will be able to add in other session from the main GOMS screen.
Chrome is the preferred browser and ensure the pop-up blocker is not on.