Here is the JS error in the console:
Uncaught TypeError: Cannot read property ‘indexOf’ of null
at Object.onUpdate (editor.min.js?ver=2.3.2:2)
at Object.success (editor.min.js?ver=2.3.2:2)
at i (load-scripts.php?c=1&load[]=underscore,shortcode,utils,jquery-core,jquery-migrate,backbone,wp-util,wp-backbone,media-models,moxiejs,plupload,wp-plupload,jqu&load[]=ery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable&ver=4.9.8:10)
at Object.fireWith [as resolveWith] (load-scripts.php?c=1&load[]=underscore,shortcode,utils,jquery-core,jquery-migrate,backbone,wp-util,wp-backbone,media-models,moxiejs,plupload,wp-plupload,jqu&load[]=ery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable&ver=4.9.8:10)
at Object.e.(/wp-admin/anonymous function) [as resolve] (https://mytheme.multisite.local/wp-admin/load-scripts.php?c=1&load%5B%5D=underscore,shortcode,utils,jquery-core,jquery-migrate,backbone,wp-util,wp-backbone,media-models,moxiejs,plupload,wp-plupload,jqu&load%5B%5D=ery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable&ver=4.9.8:10:29192)
at common.min.js?ver=2.3.2:2
at Array.forEach (<anonymous>)
at success (common.min.js?ver=2.3.2:2)
at Object.i.success (common.min.js?ver=2.3.2:2)
at i (load-scripts.php?c=1&load[]=underscore,shortcode,utils,jquery-core,jquery-migrate,backbone,wp-util,wp-backbone,media-models,moxiejs,plupload,wp-plupload,jqu&load[]=ery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-sortable&ver=4.9.8:10)
