This is a classic issue caused by unintentionally hiding elements on specific screen sizes (in this case, mobile) through CSS. Since you made theme edits previously, the most likely culprit is custom CSS code that you added.

Shopify Markets Pro is like a special helper for selling internationally.Money Stuff (Duties & Taxes): This helper automatically figures out and collects any extra fees (like import taxes) your international customers need to pay when they buy. This ...