Hey @derher,
Subscriptions do require an account in order to purchased (so there is a way to track and manage/charge those subscriptions), so unless I’m misunderstanding that other issue, it sounds like that is working as intended.
Though, for the main issue, if you have the “Enable PayPal Standard for Subscriptions” option enabled in the PayPal Standard gateway settings and this issue still occurs when logged into an account (that can purchase a subscription product), I’d suggest testing with just WooCommerce and Subscriptions active (along with a default theme) and if the issue still occurs, you can report it to the devs here:
https://github.com/woocommerce/woocommerce-gutenberg-products-block/issues