I’ve just found out this problem. Installed Merch Theme from the site library. The Back To Top button works well in desktop mode. However, the button under mobile mode will add automatically “/checkout” to its url by it self. So every time hitting the back to top button on a mobile device it will bring me to the cart. If I disabled WooCommerce, the problem went away.
I’ve also tried disabling all other plugins, and left only the default plugins come with Merch Theme. The problem stayed the same, because Merch is a WooCommerce theme with WooCommerce enabled.
How could I fix this problem, as I actually want to keep this Back to Top button. Thank you very much!