Remote instance does not support DRD and openssl warning

Hi,
I cannot get DRD to connect to all the agents.

Once I paste the token in the remote website's drd-agent-authorize, grant access, get back to my DRD but still see the "Make sure you are logged in at..." in the Domain column of Domains page.

My error log shows lots of similar errors, but basically they are:

Warning: openssl_cipher_iv_length(): Unknown cipher algorithm
Warning: openssl_encrypt(): Unknown cipher algorithm

And

Remote instance does not support DRD.
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I've tried different combinations of encryption methods (configuration, env variable, connection to core via token or via user/pass) and different projects on different servers, but the result is always the same. O

Any clue? Thanks!! =)

More details:
- Encryption profile is set with Real AES module
- Openssl is installed (OpenSSL 1.1.0)
- PHP 7.1.28 on nginx/1.14.0