The previous fix SERVER-89930 only checks if the densifying field equals to 'partitionByFields'. In AF-969, the problematic pipeline has the densifying field nested in 'partitionByFields'. For example:

{
  "$densify": {
  "field": "_id.date",
  "partitionByFields": [
    "_id"
  ],
},

 
The fix to update the uassert to apply the same check as 5733306 does.