hmm, looks like some mismatch: in yoiur config you define ECDH, but in your screenshot
i see DH configured (please compare your screenshot with the ssllabs-link i provided, esp.
the cipher-suites/handshake - part.

should be:

TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (0xc030) ECDH 256 bits (eq. 3072 bits RSA) FS

is:
TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (0xc030) DH 4096 bits



your openssl-version seems to be OK.

did you compiled nginx with your own version of openssl?

if not, what gives "openssl version" ?