When we have a query that uses positional projection on an array, the positional projection is serialized as, for example,

{ sub: { $id.$: true } }

whereas the original (valid) syntax is

{ sub.$id.$: true }

This results in this re-parse error:

Was not able to re-parse queryStats key when reading queryStats. Status: Location31325: Unknown expression $id.$ 

The test dbref3.js caught this bug and should be re-enabled when it's fixed.