Hello,
Navigate to Appearance > Menu > in the menu settings, set the display location to the mobile side menu, and check the issue.
Screenshot for clarification: https://postimg.cc/145FN2V0
Also, you need to make sure that the “http” or “https” used in the URL must be the same in both “WordPress Address (URL)” and “Site Address (URL)” from Settings >> General.
If the issue still remains, deactivate the third-party plugins on your site and check how it works. If the issue still persists, share the WP login details so I can check and give you a possible solution.
Best Regards,