Popup window from Js SDK is blocked by browser

[listendev]

We are using the official js sdk on our website:

https://www.paypal.com/sdk/js?client-id=

Smart Payment Button used to work well with a separate pop up window for our customers to make payment.

But today we found that the popup window is blocked, like this:

And this is the warning message we see in chrome's dev console:

It falls back to an modal on the same page of our payment page, which works. But the empty popup window is quite annoying. 

We haven't changed code related to paypal payment recently. 

Is there anything changed on PayPal js sdk?

[exitdoors]

I have exactly the same issue. I have no idea what to do.