Child entity showing updated value in the OriginalValue property in the Entity Framework Core Audit Trail

Question

I am working on a .NET 6 application with EF Core. I have to implement Audit Trail in the project. One of the models of my project is:

public class SystemSpecification : AuditableEntity, IAggregateRoot
{
    public int StudyType { get; set; }
    public string StudyNumber { get; set; }
    public string? Location { get; set; }
    public string? Room { get; set; }
    public string? ModelNumber { get; set; }
    public string? SerialNumber { get; set; }
    public virtual ICollection<SystemSpecificationSetPoint> SetPoints { get; set; }
}

SystemSpecificationSetPoint model is:

public class SystemSpecificationSetPoint : AuditableEntity, IAggregateRoot
{
    public int Type { get; set; }
    public string? Value { get; set; }
    public string? AcceptableRange { get; set; }
    public Guid SystemSpecificationId { get; set; }
    public virtual SystemSpecification SystemSpecification { get; set; }
}

I am writing an HttpPut end point and need to Audit the values which are updated. My end point is :

public async Task<ApiResponse<bool>> Update(UpdateSystemSpecificationRequest request, CancellationToken cancellationToken)
{
    var systemSpecificationToUpdate = await _dbContext.SystemSpecifications
        .Where(x => x.Id == request.Id).FirstOrDefaultAsync();

    _mapper.Map(request, systemSpecificationToUpdate);
        
    _dbContext.SystemSpecifications.Update(systemSpecificationToUpdate);

    await _dbContext.SaveChangesAsync(Guid.Parse("b8b8362e-adfd-4e2f-838b-e6440b60dab3"));

    return new ApiResponse<bool>() { HasError = false, Result = true };
}

My SaveChangesAsync method is:

public virtual async Task<int> SaveChangesAsync(Guid? userId = null)
{
    OnBeforeSaveChanges(userId);

    var result = await base.SaveChangesAsync();
    return result;
}

private void OnBeforeSaveChanges(Guid? userId)
{
    ChangeTracker.DetectChanges();
    var auditEntries = new List<AuditEntry>();

    var changedEntities = ChangeTracker.Entries();

    foreach (var entry in ChangeTracker.Entries())
    {
        if (entry.Entity is Audit || entry.State == EntityState.Detached || entry.State == EntityState.Unchanged)
            continue;
        var auditEntry = new AuditEntry(entry);
        auditEntry.TableName = entry.Entity.GetType().Name;
        auditEntry.UserId = userId.Value;
        auditEntries.Add(auditEntry);
        foreach (var property in entry.Properties)
        {
            string propertyName = property.Metadata.Name;
            if (property.Metadata.IsPrimaryKey() || property.Metadata.IsForeignKey())
            {
                auditEntry.KeyValues[propertyName] = property.CurrentValue;
                continue;
            }
            switch (entry.State)
            {
                case EntityState.Added:
                    auditEntry.AuditType = Domain.Entities.Enums.AuditTypeEnum.Create;
                    auditEntry.NewValues[propertyName] = property.CurrentValue;
                    break;
                case EntityState.Deleted:
                    auditEntry.AuditType = Domain.Entities.Enums.AuditTypeEnum.Delete;
                    auditEntry.OldValues[propertyName] = property.OriginalValue;
                    break;
                case EntityState.Modified:
                    if (property.IsModified)
                    {
                        if (!string.Equals(property.OriginalValue?.ToString(), property.CurrentValue?.ToString()))
                        {
                            auditEntry.ChangedColumns.Add(propertyName);
                            auditEntry.AuditType = Domain.Entities.Enums.AuditTypeEnum.Update;
                            auditEntry.OldValues[propertyName] = property.OriginalValue;
                            auditEntry.NewValues[propertyName] = property.CurrentValue;
                        }
                    }                        
                    break;
            }
        }
    }
    foreach (var auditEntry in auditEntries)
    {
        Audit.Add(auditEntry.ToAudit());
    }
}

Currently, the values in the SystemSpecificationSetPoints tables are:

I am changing the "Value" column values in the update API. I am sending the following payload to the HttpPut end point:

{
  "id": "B6AA41F8-803A-428E-3035-08DB3FEBDA44",
  "studyType": 1,
  "studyNumber": "studyNumberUpdated",
  "location": "locationUpdated",
  "room": "room",
  "modelNumber": "modelNumberUpdated",
  "serialNumber": "serialNumberUpdated",
  "equipmentTypeId": "4244B553-863E-401B-9331-08DB2ACFFFBF",
  "equipmentClassification": 1,
  "equipmentClassificationValue": "equipmentClassificationValueUpdated",
  "setPoints": [
    {
      "Id": "15693D8B-CF4A-42EC-D784-08DB466504DF",
      "type": 1,
      "value": "-500",
      "acceptableRange": "-50 to -100"
    },
{
      "Id": "288BAB37-BA86-4256-489F-08DB4BE559BD",
      "type": 2,
      "value": "-500",
      "acceptableRange": "-50 to -100"
    },
{
      "Id": "58C87D4A-EAD9-4B2E-69E0-08DB4BE7AFB4",
      "type": 3,
      "value": "-500",
      "acceptableRange": "-50 to -100"
    }
  ],
  "comment": "string",
  "criteriaMet": 0
}

When I send this payload and look into the Original and Current values of the "Value" column (Child Table Column) in the change tracker, I get the updated value in both the Original and Current values. Because of this the EF does not consider this as change and I am unable to log it.

The Save call is not yet executed but the child table values are already updated. Can someone help me to resolve this issue. I believe I am missing something very minor/basic here but any help would me much appreciated.