When you purchase a product on JVZoo, the JVZoo checkout screen asks for two email addresses: your contact email and your PayPal email address. Your contact email address is the email address that is used to store your purchases.
If you enter a different email address there or accidentally make a typo there, the system will create a new customer account for this purchase.
If you intended to have two customer accounts for a specific reason and you would like to keep your customer accounts separate, you can use two (or more) different web browsers for each login email otherwise the system gets confused as to which account to use for your login.
Using separate browsers dedicated to each email address will get rid of any login issues.