Strange behaviour with MongoDB sort operation - database

Question

Here is the information collection and sample data:
Query to get all docs with eid:abc and sorted by role.
db.information.find({eid:"abc"}).sort({role:1}) giving expected
result, but when changing eid:aaa, result is not coming in sorting
order, order is random.
On contradictory when changing sort object to role:-1, its sorting
output in ascending order but then for eid:abc output comes in
descending order. it's just behaving strangely.
Using MongoDB shell version v4.0.6 :
information =[
{_id:'110',role:'dev',eid:'aaa',info:["a","b"]},
{_id:'111',role:'tester',eid:'abc',info:["a","b","c"]},
{_id:'112',role:'admin',eid:'abc',info:["a","c"]}
{_id:'113',role:'admin',eid:'abc',info:["a","b","c"]},
{_id:'114',role:'dev',eid:'abc',info:["a","b","c"]},
{_id:'115',role:'admin',eid:'aaa',info:["a","b","c"]}
];
Output:
1.when .find({eid:"aaa"}).sort:{role:1}
=>
[
{_id:'115',role:'admin',eid:'aaa',info:["a","b","c"]}
{_id:'110',role:'dev',eid:'aaa',info:["a","b"]},
];
2.when .find({eid:"abc"}).sort:{role:1}
=> [
{_id:'111',role:'tester',eid:'abc',info:["a","b","c"]},
{_id:'114',role:'dev',eid:'abc',info:["a","b","c"]}
{_id:'112',role:'admin',eid:'abc',info:["a","c"]}
{_id:'113',role:'admin',eid:'abc',info:["a","b","c"]}];
3.when .find({eid:"aaa"}).sort:{role:-1}
=>
[{_id:'110',role:'dev',eid:'aaa',info:["a","b"]}
{_id:'115',role:'admin',eid:'aaa',info:["a","b","c"]}]
4.when .find({eid:"abc"}).sort:{role:-1}
=>
[{_id:'113',role:'admin',eid:'abc',info:["a","b","c"]},
{_id:'112',role:'admin',eid:'abc',info:["a","c"]},
{_id:'111',role:'tester',eid:'abc',info:["a","b","c"]},
{_id:'114',role:'dev',eid:'abc',info:["a","b","c"]}]

Answer 1

This is what I got with a similar environment using Mongo Shell. The sort works fine for all four cases.
Note that the find query filter is on the field eid and the sort is applied on the field role.
> db.sorts.find()
{ "_id" : "110", "role" : "dev", "eid" : "aaa", "info" : [ "a", "b" ] }
{ "_id" : "111", "role" : "tester", "eid" : "abc", "info" : [ "a", "b", "c" ] }
{ "_id" : "112", "role" : "admin", "eid" : "abc", "info" : [ "a", "c" ] }
{ "_id" : "113", "role" : "admin", "eid" : "abc", "info" : [ "a", "b", "c" ] }
{ "_id" : "114", "role" : "dev", "eid" : "abc", "info" : [ "a", "b", "c" ] }
{ "_id" : "115", "role" : "admin", "eid" : "aaa", "info" : [ "a", "b", "c" ] }
> db.sorts.find({ eid: "aaa" }).sort({ role: 1 })
{ "_id" : "115", "role" : "admin", "eid" : "aaa", "info" : [ "a", "b", "c" ] }
{ "_id" : "110", "role" : "dev", "eid" : "aaa", "info" : [ "a", "b" ] }
> db.sorts.find({ eid: "abc" }).sort({ role: 1 })
{ "_id" : "112", "role" : "admin", "eid" : "abc", "info" : [ "a", "c" ] }
{ "_id" : "113", "role" : "admin", "eid" : "abc", "info" : [ "a", "b", "c" ] }
{ "_id" : "114", "role" : "dev", "eid" : "abc", "info" : [ "a", "b", "c" ] }
{ "_id" : "111", "role" : "tester", "eid" : "abc", "info" : [ "a", "b", "c" ] }
> db.sorts.find({ eid: "aaa" }).sort({ role: -1 })
{ "_id" : "110", "role" : "dev", "eid" : "aaa", "info" : [ "a", "b" ] }
{ "_id" : "115", "role" : "admin", "eid" : "aaa", "info" : [ "a", "b", "c" ] }
> db.sorts.find({ eid:"abc" }).sort({ role: -1 })
{ "_id" : "111", "role" : "tester", "eid" : "abc", "info" : [ "a", "b", "c" ] }
{ "_id" : "114", "role" : "dev", "eid" : "abc", "info" : [ "a", "b", "c" ] }
{ "_id" : "112", "role" : "admin", "eid" : "abc", "info" : [ "a", "c" ] }
{ "_id" : "113", "role" : "admin", "eid" : "abc", "info" : [ "a", "b", "c" ] }