No, but from looking at Certificate Transparency logs it looks like they switched from RSA to ECDSA keys last week. I would expect Windows 2016 to be able to handle that fine. But it certainly looks like a recent change on the Let's Encrypt side.
Their API Announcements usually are much more around their validation connections, they don't do much announcing of changes to the API endpoint, sometimes not even even when I've or others have asked about it. Though sometimes they have.
The fact that the post this was split off of was also Windows Server 2016, and also started having problems connecting to the API at about the same time, is… awfully suspicious.