Does this same issue occur if you use our free Storefront theme?
https://woocommerce.com/storefront/
My hunch is that Astra Pro is causing the issue, so try turning on Storefront (on a staging site if possible) and testing using that. If it works in Storefront but not using Astra Pro, that’ll be a good indication your theme is causing the issue.
If it’s bunched up in Storefront as well, it could be a plugin conflict. The best way to determine this is to disable all plugins except for WooCommerce, then test by opening the checkout page again.
If you’re not seeing the same problem, then you know the problem was with one of the plugins. To figure out which plugin is causing the problem, reactivate your other plugins one by one, testing after each, until you find the one causing conflict.
You can find a more detailed explanation on how to do a conflict test here.