This happens when you have more than one account in my.presonus.com with some products registered to one account and others registered to another. In your case, you have Studio One Artist under one login and Studio One Prime under another.
It appears as you bought acquired some new add-ons, products purchases on the presonus webstore will ask you which license are the add-ons are for. If you mistakenly chose the incorrect Studio One License, then the account that license is associated with is where the newly purchased add-ons go.
Why do you have multiple accounts? If the email address behind any of social media login buttons are not the same, then you will get a new account with each one, We have no way of knowing the two accounts are associated with each other because the email accounts are not the same.
In situations like this we ask that you contact support so someone can assist you with sorting this out and we can confirm which email address you prefer to use so we can consolidate all of your products into a single login so you don't have this issue.
Logon to your http://my.presonus.com
account and click Support and there you can open a support request and we'll get you sorted out.