I'm having the same problem. Works OK in sandbox, but not in production. Now, it seems random. First I thought that was a Chrome related issue, because on Safari was working OK. Next day, it worked OK using any browser. Today, it stopped working using both browsers. An hour later, it worked OK in Chrome and not in Safari. And now, it's working OK using both browsers. However, I noticed the problem because I lost 3 customers that got the collapsing PayPal login window. I've sent a support message with the details. But no answer so far. I'll keep checking. Regards.
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