Mongodb TTL Index not expiring documents from collection


I have TTL index in collection fct_in_ussd as following

db.fct_in_ussd.createIndex(     {"xdr_date":1},     { "background": true, "expireAfterSeconds": 259200} )   {     "v" : 2,     "key" : {         "xdr_date" : 1     },     "name" : "xdr_date_1",     "ns" : "appdb.fct_in_ussd",     "background" : true,     "expireAfterSeconds" : 259200 } 

with expiry of 3 days. Sample document in collection is as following

{     "_id" : ObjectId("5f4808c9b32ewa2f8escb16b"),     "edr_seq_num" : "2043019_10405",     "served_imsi" : "",     "ussd_action_code" : "1",     "event_start_time" : ISODate("2020-08-27T19:06:51Z"),     "event_start_time_slot_key" : ISODate("2020-08-27T18:30:00Z"),     "basic_service_key" : "TopSim",     "rate_event_type" : "",     "event_type_key" : "22",     "event_dir_key" : "-99",     "srv_type_key" : "2",     "population_time" : ISODate("2020-08-27T19:26:00Z"),     "xdr_date" : ISODate("2020-08-27T19:06:51Z"),     "event_date" : "20200827" } 

Problem Statement :- Documents are not getting removed from collection. Collection still contains 15 days old documents.

MongoDB server version: 4.2.3

Block compression strategy is zstd

storage.wiredTiger.collectionConfig.blockCompressor: zstd

Column xdr_date is also part of another compound index.