After polyfill.io was transferred to a somewhat unknown company, Fastly have set up a drop-in replacement. You just need to update your polyfill.io call to polyfill-fastly.io.
Of course, now might also be the time to reevaluate loading random third-party JS code into your application.
Speaking of random third-party JS code, do you know of anything supporting this is actually being run by Fastly, other than it being in the domain name? I did some minor sleuthing here but no clear support yet: https://github.com/polyfillpolyfill/polyfill-service/issues/...
The service was announced by Fastly in supplier communication. I’d post the message here, but it’s got a big “Confidential - subject to NDA” message at the top. But I don’t think I’m breaking NDA by saying that it’s available.