Advanced checkout and no 3DS information in the response

[Partex]

Hello Guys,

We have a running PayPal Advanced Checkout integration for card payments in US. 

For most of the time the payments work well, but sometimes we are receving an unusual authentication result in the response.

It does not contain no enrollment status or any other information, like below:

"authentication_result":{"liability_shift":"NO"},

We are not sure what to do with it, as it doesn matches the responses in the table here https://developer.paypal.com/docs/checkout/advanced/customize/3d-secure/response-parameters/ 

Should we accept this response and continue with the transaction, ask for retry or reject it?

Do you have any suggestions when that result appears?