This is the expected behavior of vRNI.
Since new API for controller syslog configuration is introduced from NSX 6.2, old API is deprecated in current NSX. However, vRNI which is released before NSX 6.4.2 uses old API. Hence, if you use NSX 6.4.2 or later and edited controller syslog configuration from GUI or by new API, vRNI fails to obtain the configuration by old API.
Workaround:
No workaround