This is a known issue and fixed in AEM 6.5
For now, you can overlay "/libs/dam/cfm/models/console/components/models/datasources/childdatasource/childdatasource.jsp"
Change line 159 from
String sql = "SELECT * FROM [cq:Page] AS p WHERE p.[jcr:path] LIKE '"+pathExpression+"' ORDER BY [jcr:path]";
To
String sql = "SELECT * FROM [cq:Page] AS p WHERE ISDESCENDANTNODE(p,'/conf') AND p.[jcr:path] LIKE '"+pathExpression+"' ORDER BY [jcr:path]";
Also, increase the limit reads to a higher number from [1] till you stop getting the warning
[1] http://<host>:<port>/system/console/jmx/org.apache.jackrabbit.oak%3Aname%3Dsettings%2Ctype %3DQueryEngineSettings