ORA-01017: invalid username/password; logon denied from sql developer but sqlplus logins
The problem was that I had too many instant clients and Oracle clients on my machine (one oracle client 'x86').

The instant clients were too old.

The only working instant client for me is the '12.1.0.2.0'.

I downloaded:


instant client basic lite win64 12.1.0.2.0
instant client jdbc win64 12.1.0.2.0
instant client sqlplus win64 12.1.0.2.0


fixed the PATH variable with the path I extracted the instant client '12.1.0.2.0' and removed all others from it.

In the end I set up the environment variable TNS_ADMIN pointing to my sqlnet.ora and tnsnames.ora. I think this TNS_ADMIN is not necessary.