JS Error when trying to add users to Section Editor group

I’m getting the following JS error when trying to add users to an editing group:

group-editor.min.js:4 Uncaught ReferenceError: buse_site_users is not defined
    at a.(anonymous function).(anonymous function).source (../wp-content/plugins/bu-section-editing/js/group-editor.min.js:4:355)
    at a.(anonymous function).(anonymous function)._search (../wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load%5B%5D=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load%5B%5D=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407:5252)
    at a.(anonymous function).(anonymous function)._search (../wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load%5B%5D=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load%5B%5D=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22:1032)
    at a.(anonymous function).(anonymous function).search (../wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load%5B%5D=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load%5B%5D=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407:5123)
    at a.(anonymous function).(anonymous function).search (../wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load%5B%5D=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load%5B%5D=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22:1032)
    at a.(anonymous function).(anonymous function).<anonymous> (../wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load%5B%5D=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load%5B%5D=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407:4925)
    at c (../wp-admin/load-scripts.php?c=0&load%5B%5D=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load%5B%5D=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load%5B%5D=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22:5409)
source @ group-editor.min.js:4
_search @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407
(anonymous) @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22
search @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407
(anonymous) @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22
(anonymous) @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407
c @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22
setTimeout (async)
_delay @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22
_searchTimeout @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407
(anonymous) @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22
input @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:407
h @ load-scripts.php?c=0&load[]=jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-resizable,jquery-ui-draggable,jquery-ui-button,jquery-ui-position,jque&load[]=ry-ui-dialog,wpdialogs,hoverIntent,common,admin-bar,jquery-ui-tabs,svg-painter,heartbeat,wp-auth-check,jquery-ui-sortable,jquery&load[]=-ui-slider,jquery-touch-punch,iris,wp-color-picker,jquery-ui-menu,wp-a11y,jquery-ui-autocomplete&ver=4.8.5:22
dispatch @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,utils,farbtastic&ver=4.8.5:3
r.handle @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,utils,farbtastic&ver=4.8.5:3

Any ideas what might be happening here?