An aggregation that runs against a collection that has been recently created or that is concurrently created may fail with QueryPlanKilled.

This is the sequence of operations run in a jstest that has triggered the error. The aggregation uses $out, but we assume the issue would occur with any aggregation that is not collectionless.

// create the collection through an insert with write concern {w:1}
coll.insert({x:1}, {writeConcern: {w:1}})

// run aggregation with readConcern: 'majority'
coll.aggregate([{$match: {}},{$out: "collOut"}], {readConcern: {level:'majority'}})

Reasoning

During aggregation, all involved collections are acquired up front, then released, and re-acquired when pipeline execution starts.
It could happen that the aggregation's target collection appears only after the second acquisition. At that point, the operation would fail with QueryPlanKilled, because a collection participating in the aggregation cannot be created while the aggregation is in progress.