I am a representative of hosting company, and our clients have problems with certificate issue from network 22.214.171.124/24, for example last incident was with 126.96.36.199 and domain diplomtop.ru (now its work, because certificate was generated with third-arty service). When we try issue certificate from server's IP with panel VestaCP, get error 400.
This is 100% problem with IP, domains pointed correctly, if we change IP for another - certificate installation goes without any problems.
I think there are some sanctions from LE side for this IP or subnet, and i really hope that you can help solve this problem. Otherwise, we need to change addresses on a large number of servers.