Menu issues on mobile browsers cause a 404 error

I recently worked over my website www.silverstarimmigration.net. On my desktop, everything works fine (including the appearance of the links). When I browse the website on a mobile phone the links on the menu are in a strange format. For instance: The menu item is https://silverstarimmigration.net/immigration On the mobile phone it shows: https://silverstarimmigration.net/Menu#https://silverstarimmigration.net/immigration which causes a 404 error on the mobile phone. I tried all and everything but I cannot solve this issue myself. I would appreciate any tips on how to solve it. Thanks.