Firestore Mapping Issue: Why Isn't a Private Field Mapped Despite a Setter?

I have a Firestore structure where the map named lecturaBreve corresponds to the following class:

The class is defined as follows:

JAVACopied
public class BiblicalShort extends Biblical {
    private LHResponsoryShort responsorio;

    public BiblicalShort() {
    }

    public void setResponsorio(LHResponsoryShort responsorio) {
        this.responsorio = responsorio;
    }
}

The map named responsorio should be mapped to this class:

JAVACopied
public class LHResponsoryShort {

    protected Integer responsoryID;
    protected String text;
    protected Integer type;

    public Integer getResponsoryID() {
        return responsoryID;
    }

    public void setResponsoryID(Integer responsoryID) {
        this.responsoryID = responsoryID;
    }

    public String getText() {
        return this.text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public Integer getType() {
        return this.type;
    }

    public void setType(Integer type) {
        this.type = type;
    }

    // ...
}

My issue is that when mapping the Firestore response to these classes, the nested responsorio object is not mapped correctly if it is declared as a private field, even though I have defined a public setter.

Interestingly, if I declare the field as public:

JAVACopied
public LHResponsoryShort responsorio;

the mapping succeeds. I would like to understand why Firestore is not mapping the private field despite having a properly defined setter. Are private properties not being mapped when using a setter, or is something missing in my configuration?