I ran into this problem and it seemed to be triggered when 1) shipping addresses are not needed/collected and 2) the receiver account has any kind of sales tax calculations set up (deep in the PayPal settings)

I reported the issue via Merchant Technical Support on the 22nd and got this response yesterday:

"Unfortunately, the problem you're experiencing appears to be caused by technical issues within the PayPal system.

I added this account to our existing engineering ticket so that when the problem is resolved, you will be notified of its completion right away.

Our engineers are already working diligently on a solution to this problem. This ticket will remain in a "Pending Fix" status until you're contacted about the resolution.

I apologize for the inconvenience and thank you for your patience!"