I'm not aware of any policy changes, so my money would be on this:
https://www.paypal-status.com/api/production

Intermittent issues started popping up on their end 30+ minutes ago, and perhaps PayPal is jury rigging something on their end.

I will inquire within the company whether we made any policy changes after all, but please just check if the issue persists after an hour or two, when - hopefully - PayPal recovers. :)

That being said, I remember that we always required instant payment sources to be used via PayPal - perhaps for some reason your bank account stopped processing instant bank transfers for a while, and PayPal cannot verify it as being an "instant" payment source?
Just a thought. I'll let you know once I confirm whether or not any changes were indeed made on our end. :)

And I confirm that we've made no policy changes recently.
¯\_(ツ)_/¯