Custom Mongo queries inexplicably return zero results after upgrading to 3.0.8.RELEASE or later (spring-boot dep mgmt: 2.3.10.RELEASE or later)

I've created a repo to demonstrate the issue, at https://github.com/oliverlockwood/mongodb-issue-demonstration, based on following the guidelines at https://spring.io/guides/gs/accessing-data-mongodb/.

That repo has a clear README but I'll highlight the main points here as well.

• In terms of environment, I have a local Docker container running MongoDB version 4.2.14, mapping ports 27017 and 28017.
• The Customer model class contains a map field, like: public Map<String, DataValue> additionalData;
• There are custom read/write converters configured; we persist the map as an array of (name, value) tuples, viz:
  
• We have a custom repository implementation which allows dynamic queries to be specified (in our real use-case, via REST query payloads; in the example repo, via hard-coding in the run() method)
• The custom Mongo query we generate in the application (regardless of spring-data-mongodb version) is logged out as:
  Query: { "$and" : [{ "additionalData.name" : "a"}, { "additionalData.value" : "b"}]}, Fields: {}, Sort: {}
• With spring-boot version 2.3.9.RELEASE (therefore spring-data-mongodb version 3.0.7.RELEASE) an entry is found as expected by this query
• With spring-boot version 2.3.10.RELEASE or higher (therefore spring-data-mongodb version 3.0.8.RELEASE or higher) no results are found
• Directly querying Mongo via the console, i.e.
  db.getCollection('customer').find({ "$and" : [{ "additionalData.name" : "a"}, { "additionalData.value" : "b"}]})
  finds an entry as expected

I therefore conclude this is a regression in spring-data-mongodb, but I can't for the life of me figure out why it stops returning results.

I hope this in combination with the repo is enough context for you to investigate; please advise if you need me to provide any more information.

Many thanks!