gs.addErrorMessage() placed in script include returns twice onClick of 'assignment_group' field on incident table.
Onclick of assignment_group executes "group query" business rule twice: one for each call to the following tables:
This in-turn triggers the script include twice. Function call to sys_ui_recent_selection cannot be escaped.
Create those error messages in onChange client script for 'assigned_to' field instead of script include call from server side.