Dropdown menu not functioning correctly

Dropdown menu not functioning correctly

Pls refer to the information below and advise thanks.

JSP page

External jquery version: 3.4.0
Jquery UI JS version: 1.12.1
Jquery UI CSS version: 1.12.1
Web Browser: Chrome




After selecting a year from the dropdown menu, it does not appear in the box.There is no error in the console as well. However if I double click in the dropdown menu, the error below shows up in the console.