Jetzt hätte ich doch was gefunden in der Webkosole:
Uncaught TypeError: $(...).live is not a function
at HTMLDocument.<anonymous> (admin-scripts.js?ver=5.5:173)
at i (load-scripts.php?c=1&load[chunk_0]=jquery,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-draggable,jquery-ui-slider,jquery-touch-punch,iris&ver=5.5:2)
at Object.fireWith [as resolveWith] (load-scripts.php?c=1&load[chunk_0]=jquery,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-draggable,jquery-ui-slider,jquery-touch-punch,iris&ver=5.5:2)
at Function.ready (load-scripts.php?c=1&load[chunk_0]=jquery,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-draggable,jquery-ui-slider,jquery-touch-punch,iris&ver=5.5:2)
at HTMLDocument.J (load-scripts.php?c=1&load[chunk_0]=jquery,jquery-ui-core,jquery-ui-widget,jquery-ui-mouse,jquery-ui-draggable,jquery-ui-slider,jquery-touch-punch,iris&ver=5.5:2)