On v6.0: const c = db.bf27387; c.drop(); c.save({_id: 0, array: [ "abc" ]}); const res = c.aggregate( [{$project: { "obj.obj.array" : 1}}, {$match: {$expr: {$getField: {$literal: "array" }}}}]); // The bug caused the query above to return { "_id" : 0 } instead of no documents. assert.eq(0, res.toArray().length); Mongo v6.0 will erroneously generate the following plan for the aggregation: "winningPlan" : { "stage" : "PROJECTION_DEFAULT" , "transformBy" : { "_id" : true , "obj" : { "obj" : { "array" : true } } }, "inputStage" : { "stage" : "COLLSCAN" , "filter" : { "$expr" : { "$getField" : { "field" : { "$ const " : "array" }, "input" : "$$CURRENT" } } }, "direction" : "forward" } }, The filter is merged into the collscan, putting the filter before the projection. This is problematic because the semantics of the filter are different when operating on the full (unprojected) document. The correct plan, produced by v6.1, is: { "explainVersion" : "1" , "stages" : [ { "$cursor" : { "queryPlanner" : { "namespace" : "test.bf27387" , "indexFilterSet" : false , "parsedQuery" : { }, "queryHash" : "92148A8F" , "planCacheKey" : "92148A8F" , "maxIndexedOrSolutionsReached" : false , "maxIndexedAndSolutionsReached" : false , "maxScansToExplodeReached" : false , "winningPlan" : { "stage" : "PROJECTION_DEFAULT" , "transformBy" : { "_id" : true , "obj" : { "obj" : { "array" : true } } }, "inputStage" : { "stage" : "COLLSCAN" , "direction" : "forward" } }, "rejectedPlans" : [ ] } } }, { "$match" : { "$expr" : { "$getField" : { "field" : { "$ const " : "array" }, "input" : "$$CURRENT" } } } } ],...}