Apparantly these two lines (below) in ConversationUtils.java cause null to be shown instead of username.
Line 245 and same line at 329
from = message.getToJID().getResource();
This is basically because earlier resource was stored in fromjid/tojid column of database.
But now resource is stored in fromjidresource and tojidresource columns instead of fromjid/tojid.
So above two lines always returns null and hence logs also show null.
Monitoring Service plugin 1.3.0, also older versions as reported
Thanks for the assist, fixed it.