I’m having the same problem, and have been for some time.
We just launched a site we’ve been working on where, from day one, we would get that error often. Not all the time, but at least 50% of the time. It’s still happening, so I set out to test it.
I just finished setting up a test site using only WordPress 4.7, WooCommerce, and PayPal Powered by Braintree plugins with the plain Storfront theme. On this site, I’m getting this error every single time.