In v6.0, the fle2_contention_kill_parent.js can encounter WriteConflict errors when performing an encrypted update that follows a previous killed encrypted update operation (provided that the same contention factor value is coincidentally selected).

This is because per SERVER-70247, if an ongoing internal transaction gets cancelled by a killOp, the transaction just lingers in an idle state until later reaped by another background job. If the killed transaction has managed to write to the ESC collection, then the following transaction can potentially write the same _id value if the same contention factor is used, which causes a write conflict on the _id index.