Mobile Navigation Menu Not Working after User login

Hi,

Mobile version of my website not working well. The main issue is as follows:

The menu bar (on mobile device) is not responsive when a user successfully login. However, it responds perfectly when no user login. Please how can I fix this? Thank you very much.
My website is http://www.sitibe.com. Please visit the website on any mobile device and click on the menu bar, then you will understand my issue better.

Thank you once again.