This is probably one of the strangest and most frustrating issues I've come across. We have a website that is an online shop using, WordPress and WooCommerce.
A lot of their marketing is done via their Instagram page. When the website is opened from the Instagram app it opens in Instagram's in-app browser. Everything seems to work fine until you get to the checkout. The payment options section is greyed out and the card fields are squashed. If you open the same page on desktop browsers or mobile browsers this section is fine and works as it is supposed to.
I have tried moving this to staging and disabling all of the plugins except WooCommerce and also with the Twentynineteen and Storefront themes and the issue occurs with all of these configurations.
I know that other WordPress and WooCommerce website don't experience this issue so I am at a bit of a loss trying to find out what is causing it.