We've had several reports since yesterday about PayPal checkout sporadically getting hung up or stalling out at various points. We have reported the issue to PayPal MTS (Merchant Technical Support), so they can look into it further. We're also seeing other reports around the Web since yesterday about trouble with PayPal involving other services unrelated to ours.
In testing this with the affected sellers' products, we're only sporadically getting a stall-out, and at varying points -- sometimes after clicking the Pay Using PayPal button in our cart, sometimes upon arriving at the PayPal checkout site and attempting to log into our PayPal account, sometimes after clicking the Complete Purchase button on the PayPal checkout site -- while at other times everything works just fine.
Once a buyer clicks the PayPal checkout button in their cart, at that point we're just waiting on the PayPal checkout site to respond, so we can finish redirecting the buyer there to pay for their order. As such, a stall at that point indicates PayPal's end isn't responding yet, and of course anything happening after the redirection to checkout would be entirely at PayPal's end.
All of that suggests some issue with PayPal's system -- possibly just high traffic causing their site to bog down sometimes, or perhaps some other emergent glitch -- hence our opening that ticket about it with PayPal MTS (Case # 12440024), who have now acknowledged the issue at their and confirmed they now have developers assigned to resolve it. We'll followup here to confirm if and when they say the issue is resolved at their end.