db={transaction:[{/** doc 1*/TransactionStatus:[{StatusType:2},{StatusType:1}]},{/** doc 2*/TransactionStatus:{StatusType:[2,1]}},{/** doc 3 - this one has an issue*/TransactionStatus:{StatusType:1}}]}

db.transaction.find({$expr:{"$eq":[{"$arrayElemAt":["$TransactionStatus.StatusType",-1]},1]}})