Thank you for contacting Syncfusion support.
We have checked the reported issue with our latest version (v16.4.46) by rendering the EJ2 – Menu (vertical orientation) inside the Sidebar and the sub menu items are shown properly on mouse hover in
our end. For your convenience, we have attached the demonstrated sample and hosted a live demo.
Could you please check again once cleaned the browser cache and get back to us? If still issue persists, we would like to know the following details.
1. Please share your Essential Studio product version that you are currently using.
2. Could you please ensure that the assemblies and assets (CSS & scripts) references are referred from same product version?
3. Please share the code snippet or the details if you did any customization with Menu or Sidebar. If possible, please replicate your issue with the above sample and get back to us.
Could you please get back to us with the above information so that we can analyze based on that and provide you a solution quickly? The information provided would be great help for us to proceed further.