The output of a query like

{aggregate: "fuzzer_coll", pipeline: [ { "$sort" : { "_id" : 1 } }, { "$group" : { "_id" : "$obj.obj", "num" : { "$stdDevPop" : "$obj.num" } } } ], cursor: {   }, maxTimeMS: 30000}

in QueryTester (seed 1771702139010) has changed slightly between commit 53bcce271b617144372d7d2d08163b917889244a and now.

{"_id":null,"array":[],"date":null,"num":30140.045988782727},

vs

{"_id":null,"array":[],"date":null,"num":30140.045988782724},

While the baseline value is measured against 5.0, the values from trunk agreed with the value generated by 5.0 through commit 53bcce, but this has since changed.

It's notable that all these queries contain $group or $bucket in conjunction with $stdDevPop or $stdDevSamp. It's likely that the interaction between these operators has changed slightly, causing these small numerical value differences.