I spoke the cx_oracle PM about this.
1804 probably means a timezone setting issue. He recommended to use the 19c client, but in particular, do the installation via RPM (
http://yum.oracle.com/repo/OracleLinux/OL7/oracle/instantclient/x86_64/index.html ) because it takes cares of any setup etc.
In terms of why it works on one but not the other, check settings for TZ and ORA_SDTZ and of course file permissions to make sure they can actually read the Instant Client files.
Since you installed into /opt/oracle it would be better using ldconfig (as mentioned in Instant Client install instructions) instead of setting LD_LIBRARY_PATH
And of course, make sure you've done everything as listed in the cx_Oracle installation instructions