Mobile Menu dropdown not working in Twentythirteen

The website works fine on the desktop but there is no drop down available in the menu when used on mobile device. It had been working earlier but I don’t when it stopped working until I checked it a few days ago. I’ve removed the Jetpack plugin, checked there is no javascript errors, updated with <h3>menu</h3>, etc as advised in the other similar posts but these are still not working. Please help. My site is https://www.hilifehub.com

Thank you