I also have this issue. The console error it generates for me is:
media-upload.min.js?ver=5.4.2:2 Uncaught ReferenceError: wpActiveEditor is not defined
at Object.window.send_to_editor (media-upload.min.js?ver=5.4.2:2)
at Object.insert (media-editor.min.js?ver=5.4.2:2)
at Object.insertGallery (admin-gallery.js?ver=2.2.3:198)
at HTMLButtonElement.<anonymous> (admin-gallery.js?ver=2.2.3:315)
at HTMLDivElement.dispatch (load-scripts.php?c=1&load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-draggable,jquery-ui-position&ver=5.4.2:3)
at HTMLDivElement.r.handle (load-scripts.php?c=1&load[chunk_0]=jquery-core,jquery-migrate,utils,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-draggable,jquery-ui-position&ver=5.4.2:3)
And will, of course, replicate each time I hit the “Insert gallery into post” button.