Reports

(It's more a comment, but using "comment" is limited.)

If you use openssl, e.g.

openssl s_client -dtls1_2 -connect californium.eclipseprojects.io:5684 -cipher ECDHE-ECDSA-AES128-GCM-SHA256

that prints

SSL-Session:
    Protocol  : DTLSv1.2
    Cipher    : ECDHE-ECDSA-AES128-GCM-SHA256
    Session-ID: DF8ACBFEA82FF766892EDBEF6BDA283063FF029BE5978483A4EC4FAEBCB3B1E1
    Session-ID-ctx: 
    Master-Key: C5FE3608B349CB4155FAD5E42B9BC7CCCD3132DE07D5FD4A878091AB62EEA1A5DBF243877178A2CBF4656B61F4F9066E
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    Start Time: 1730107483
    Timeout   : 7200 (sec)
    Verify return code: 20 (unable to get local issuer certificate)
    Extended master secret: yes

Did you check your master key with the one from openssl?

79132769