N1QL execution plan

SQL++
1

We have a N1QL query is taking minutes to run, even we have an index for it. The explain shows the index is used, but it should not have as the performance indicates.

When I hint for another index, the performance improves too. Is possible that the index actually not in used? How can I tell?

select * from TA USE INDEX (company_index1) where _class = "aaa.bbb.ccc.ddd.eee"
AND idoc.header.cid = "12345"
AND idoc.header.uid = “5678”

CREATE INDEX company_index1 ON TA(_class,idoc.header.cid,idoc.header.uid,assignments.context) WHERE (_class = “aaa.bbb.ccc.ddd.eee”) USING GSI

EXPLAIN select * from TA USE INDEX (company_index1) where _class = "aaa.bbb.ccc.ddd.eee"
AND idoc.header.cid = "12345"
AND idoc.header.uid = “5678”

Shows [
{
"#operator": “Sequence”,
"~children": [
{
"#operator": “IndexScan”,
“index”: “company_index1”,
“keyspace”: “TA”,
“namespace”: “default”,
“spans”: [
{
“Range”: {
“High”: [
“successor(”")"
],
“Inclusion”: 1,
“Low”: [
""[