Query is not sargable to complex partitioned index

This is complex case, But would like to bring up issue (This is case Chubb POC reported, in POC customer OR clause values are consecutive, so replace with between).

The following query is not sargable to ix4 and makes index unusable.

create index ix4 on default(a,b) where (x=1 and (y=3 or y =4) and z = 2);
explain select a from default where a is not missing and (x=1 and (y=3 or y =4) and z = 2);
{
"requestID": "09809569-c144-4b91-a563-22c2f398cdf6",
"errors": [

{ "code": 4000, "msg": "No primary index on keyspace default. Use CREATE PRIMARY INDEX to create one." }

],
"status": "fatal",
"metrics":

{ "elapsedTime": "5.461913ms", "executionTime": "5.423896ms", "resultCount": 0, "resultSize": 0, "errorCount": 1 }

}