Hey there, @foxcote90
Bo here from Shopify Support.
I am sorry to hear that you are experiencing this issue. Have you been able to replicate it on your end? As it has occurred for three separate customers it does sound like it may be an issue. Can you confirm that the PayPal account is a merchant account? In my experience, when users add personal accounts to their Shopify stores issues like this can occur.
If this is a merchant account, I would then recommend deactivating the gateway. Once deactivated you can then add it again. This will help reconfigure the gateway with your store and prevent this from happening again.
If this error occurs once again after reconfiguring the gateway I would recommend reaching out to PayPal here so that they can investigate this on their end for you.
Let me know how this goes and if there is anything else I can assist you with, I'm happy to help!
All the Best,