The connection validation fails if SYS account is used in the agent.

Foglight Management Server (FMS) log contains such type of errors:
<error-respond>
<error-code>-34</error-code>
<error-message>Granting user privileges failed.</error-message>
<error-details>Failed to execute query on instance [agent_name], user account [sys]. Reason : [ORA-20001: ORA-65041: CONTAINER_DATA attribute for this user cannot be modified,sql:alter user SYS set container_data=ALL CONTAINER=current
ORA-06512: at "SYS.EXECUTE_IMMEDIATE", line 34
ORA-06512: at line 203
OR
<error-details>Failed to execute query on instance [agent_name], user account [sys]. Reason : [ORA-20100: Check failed - missing_advisory_privileges FET$ORA-06512: at line 316