This issue was previously reported by SagePtr on GitHub.
This article in Russian describes the problem, in short:
Two IPs, 188.8.131.52 and 184.108.40.206, that host Let’s Encrypt website (letsencrypt.org) are in the Roscomnadzor Registry of forbidden resources. Roscomnadzor did not specifically target Let’s Encrypt, rather it banned a large number of IPs in connection with other websites and Let’s Encrypt just recently moved to these two APIs (after switching hosting from Akamai Technologies, Inc. to Digital Ocean, LLC). Authors note that so far the ban affects only the website, but warns that if Let’s Encrypt certificate issuance APIs move too, they might become unavailable.
I’m not affiliated with Let’s Encrypt in any way, but as far as I know, Let’s Encrypt APIs are hosted in a co-location environment and should not change IPs so are not affected by the Russian Roscomnadzor roulette. Could someone knowledgeable confirm this?
Full article translation
Here is a full article translated to help Let’s Encrypt staff investigate the matter.