please see is there any local(content OR structure component) clientlibs which is using jquery or vanilla js to get some attribute of the dialog, is using correct coral2 or coral 3 UI specific class or not, for example in coral 2 UI we will be using
var dropdownSelection = $('span.marketingTileDropdown').find('.coral-Select-button-text')[0].innerText;
and in coral3 UI it will be
var dropdownSelection = $('span.marketingTileDropdown').find('.coral3-Select-button-text')[0].innerText;
something like the above snipet you may need to check.
NOTE: this is just an example for your reference.
hope this will help.
Umesh Thakur