Hi
I just checked and I had exactly the same errors :
2019-11-20T13:32:33+01:00 Diskstation synoscgi_SYNO.Core.Certificate.LetsEncrypt_1_create[14411]: certificate.cpp:973 syno-letsencrypt failed. 200 [new-req, unexpect httpcode]
2019-11-20T13:32:33+01:00 Diskstation synoscgi_SYNO.Core.Certificate.LetsEncrypt_1_create[14411]: certificate.cpp:1392 Failed to create Let’sEncrypt certificate. [200][new-req, unexpect httpcode]
I just updated to latest available DSM version (DSM 6.2.2-24922 Update 4) and now it works fine