In Walk-up portal, when any user checks-in the pop-up message that gets displayed after clicking "Check In" button always says "You are Number #1 in the queue" irrespective of the user's position in the queue.

 "walkup_check_in" page might be using custom widget.

 Page URL =>  https://<INSTANCE-NAME>/sp_page.do?sys_id=d2467ce1231203004f93121727bf6546&sysparm_record_target=sp_page&sysparm_record_row=1&sysparm_record_rows=1&sysparm_record_list=sys_id%3Dd2467ce1231203004f93121727bf6546

Modify the "walkup_check_in" page to use OOB widget named "Walk-up Check-In"

Widget URL => https://<INSTANCE-NAME>.service-now.com/sp_widget.do?sys_id=ca7d3c813b3a03001d132c2b54efc4bf