Nick here from Shopify!
I took a look into this for you. The footer menu did show up for me but did have some parts not there, such as the tab options seen here. A lot of themes do adapt to mobile and aren't the exact same to make the mobile experience better, so I'm thinking it could be that.
The theme has been heavily modified, would you able to confirm which theme it is exactly and I can take a closer look into this if it is a Shopify theme or if it is a theme from a third party developer. Once I know which exact theme we can see why this might be happening.
All the best,
Thanks for getting back to me. I looked into this for you and found out this is a theme developed by third-party developers who sell the theme on the Shopify theme store. It's developed by a company called Velatheme which you can see from the screenshot here. This is the contact email address they provide: email@example.com. Your best bet would be to reach out to them directly by email and explain what you did in the forum post above and they should be able to help you.
Hope this helps explain this and points you in the right direction for next steps on how to get it sorted out.