can't edit - The If-Match version is missing or not valid for the resource.

Some web browser extensions (add-ons), for example ClearURLs, remove ETag headers, which causes updates to fail. To update your distribution, disable this browser extension or turn off ETag filtering.

Thanks, it was ClearURLs causing this.

me too.

you can try "Private browsing" mode

I could not create a second CloudFront origin through the management console until I turned ClearURLs off.