Hi,
Using MongoDB version 3.6.7. Also tested on 4.0.2
Trying to create an index on two arrays using the shell:
db.test.createIndex({ "array1": 1, "array2": 1}) 
it fails with this error:
{
	"operationTime" : Timestamp(1561615657, 1),
	"ok" : 0,
	"errmsg" : "cannot index parallel arrays [accountGrp] [links]",
	"code" : 171,
	"codeName" : "CannotIndexParallelArrays",
	"$clusterTime" : {
		"clusterTime" : Timestamp(1561615657, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	}
}
However, on the logs we only see:
2019-06-27T16:07:39.901+1000 I INDEX    [conn18] build index on: test.test properties: { v: 2, key: {array1: 1.0, array2: 1.0 }, name: "index_arrays_name", ns: "test.test" }
2019-06-27T16:07:39.904+1000 I INDEX    [conn18]         building index using bulk method; build may temporarily use up to 500 megabytes of RAM
There's no failure recorded.
This limits out troubleshooting capabilities. We should logged some error on the server log.
- duplicates
- 
                    SERVER-20940 Should log createIndexes failure at level 0 -         
- Closed
 
-