"Bad Request" when using nested queries for facets

I'm having issues getting nested queries and facets to work on my Commerce catalog content types, specifically a product content and a variation content.

I'm running Find 11.1.0.3965, Commerce 9.8.1, and CMS 9.6.1.

The issue

When I try to get results from Find, I'm getting a "(400) Bad Request" (I've tried to cut out unnecessary error data):

SearchPhaseExecutionException[Failed to execute phase [query], all shards failed; 
...
Parse Failure [Failed to parse source 
..."facets":{"MyNestedObjects.NestedObjectProperty":{"terms":{"field":"MyNestedObjects.NestedObjectProperty$$string"},"nested":"MyNestedObjects"},
...
Parse Failure [facet nested path [MyNestedObjects] not found]]; }

The code

Based on the documentation (http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-Find/11/DotNET-Client-API/Searching/nested-queries/), I think I have everything configured and developed correctly.

This is done in an initialization module:

SearchClient.Instance.Conventions.NestedConventions.ForType().Add(content => content.MyNestedObjects);
SearchClient.Instance.Conventions.NestedConventions.ForType().Add(content => content.MyNestedObjects);

On the content types, I have the properties as such:

public IEnumerable MyNestedObjects
{
    get
    {
        var listOfNestedObjects = new List();
        ...
        return listOfNestedObjects;
    }
}

And I'm setting up the search and facets like this:

SearchClient.Instance.Search(Language.English)
    .For(someQueryText)
    .InFields(x => x.DisplayName)
    .InAllField()
    .TermsFacetFor(x => x.MyNestedObjects, x => x.NestedObjectProperty);
    .GetContentResult();

And an example of the indexed data on an instance of the content looks like:

..."MyNestedObjects$$nested": [
{"$type": "MyProject.Objects.NestedObject, MyProject","___types": ["MyProject.Objects.NestedObject","System.Object"
    ],"NestedObjectProperty$$string": "Some Value"
}]
...

I have also tried this all as a function call on the content types, making sure to IncludeField() the function call, but the result is the same.

So everything looks to be set up correctly, right? What gives?