Group stage in aggregation is being skipped

[Jack_Woehr]

@Stephen_Lynx

I don’t know if it’s relevant, but ‘onDisk’ can be null, and it was when it failed, I can’t tell if it failed with large amounts an non-null values for onDisk.

$group (aggregation) - MongoDB Manual v7.0

The _id expression specifies the group key. If you specify an _id value of null, or any other constant value, the $group stage returns a single document that aggregates values across all of the input documents. See the Group by Null example.