I checked the navigation sub menu items and I don’t see any issues as such. I have recorded the screencast, please take a look and let me know if I am reproducing the issue you are facing correctly.
Further inspecting the website I see that you are using X Theme version 6.3.8 and Cornerstone 3.4.5. It might cause some incompatibility issues, in that regards I suggest you to update X Theme to the most recent version X 6.4.6 and Cornerstone 3.4.6.