Why is the PayPal Checkout page greyed out?

It seems this fault has been going for years, PayPal don't know why it is and say it's our fault.
I think the checkout page is hosted somewhere else?
My regular customers don't have this problem, it's the NEW customers that can't pay. I suspect PayPal save their details so checkout is faster or pre-filled?
Does anyone have this problem?
Did anyone solve it? Ta everyone, Steve