Updating subtables adds records rather than amending existing records

I have these two models:

public class Balance1 : IAnalyticsSection
{
    public int Id { get; set; }
    public Guid DataFileId { get; set; }

    public string Side { get; set; }
    public decimal AverageHSway { get; set; }
    public decimal AverageSSpeed { get; set; }
    public decimal AverageLHSway { get; set; }
    public decimal AverageRHSway { get; set; }
    public decimal PercentAverageInLSphere { get; set; }
    public decimal PercentAverageInRSphere { get; set; }
    public decimal AverageTotalSway { get; set; }

    public virtual ICollection<Balance1Part> Parts { get; set; } = new List<Balance1Part>();
    public virtual DataFile DataFile { get; set; }
}


public class Balance1Part
{
    public int Id { get; set; }
    public int Balance1Id { get; set; }

    public int Order { get; set; }
    public decimal ConvexHullArea { get; set; }
    public decimal HSway { get; set; }
    public decimal SSpeeds { get; set; }
    public decimal LHSway { get; set; }
    public decimal RHSway { get; set; }
    public decimal PercentInLSphere { get; set; }
    public decimal PercentInRSphere { get; set; }
    public decimal TotalSway { get; set; }

    public virtual Balance1 Balance1 { get; set; }
}

In my context I have public DbSet<Balance1> Balance1 { get; set; } but nothing for Balance1Part. There will only ever be 5 Balance1Part records for each Balance1. When I enter a new record into Balance1, it successfully creates with each of the 5 parts. If I try to update Balance1 it succeeds but 5 additional part records are created. These are duplicates of the existing records.

This is is the code that enters/updates my Balance1 and Balance1Parts:

var innerBalance1File = await innerContext.Balance1.SingleOrDefaultAsync(x => x.DataFileId == dataFile.Id);

Balance1Class balance1Class = new Balance1Class();

if (innerBalance1File == null)
{
    innerBalance1File = new Balance1();
    innerBalance1File.DataFileId = dataFile.Id;
    innerBalance1File = balance1Class.Balance1Data(innerBalance1File, values);

    await innerContext.AddAsync(innerBalance1File);
}
else
{
    innerBalance1File = balance1Class.Balance1Data(innerBalance1File, values);
    innerContext.Entry(innerBalance1File).State = EntityState.Modified;
}

await innerContext.SaveChangesAsync();

This is my Balance1Calss:

public class Balance1Class
{
    public Balance1 Balance1Data(Balance1 balance1, Dictionary<string, object> values)
    {
        //Balance1 balance1 = new Balance1();
        //Balance1Part balance1Part = new Balance1Part();

        if ((values["DataType"]).Equals("Balance1R"))
        {
            balance1.Side = "R";
        }
        else
        {
            balance1.Side = "L";
        }

        balance1.AverageHSway = decimal.Parse(values["AverageHSway"].ToString());
        balance1.AverageLHSway = decimal.Parse(values["AverageLHSway"].ToString());
        balance1.AverageRHSway = decimal.Parse(values["AverageRHSway"].ToString());
        balance1.AverageSSpeed = decimal.Parse(values["AverageSSpeed"].ToString());
        balance1.AverageTotalSway = decimal.Parse(values["AverageTotalSway"].ToString());
        balance1.PercentAverageInLSphere = decimal.Parse(values["%AverageInLSphere"].ToString());
        balance1.PercentAverageInRSphere = decimal.Parse(values["%AverageInRSphere"].ToString());

        var balance1Parts = balance1.Parts;  // Gets actual balance parts: returns a list

        if (balance1Parts.Count == 0 || balance1Parts == null)
        {
            for (int i = 1; i < 6; i++)
            {
                Balance1Part balance1Part = new Balance1Part
                {
                    HSway = decimal.Parse(values["HSway" + i].ToString()),
                    SSpeeds = decimal.Parse(values["SSpeeds" + i].ToString()),
                    LHSway = decimal.Parse(values["LHSway" + i].ToString()),
                    RHSway = decimal.Parse(values["RHSway" + i].ToString()),
                    PercentInLSphere = decimal.Parse(values["%InLSphere" + i].ToString()),
                    PercentInRSphere = decimal.Parse(values["%InRSphere" + i].ToString()),
                    TotalSway = decimal.Parse(values["TotalSway" + i].ToString()),
                    ConvexHullArea = decimal.Parse(values["ConvexHullArea" + i].ToString()),
                    Order = i,
                };
                balance1.Parts.Add(balance1Part);
            }
        }
        else
        {
            foreach (var balance1Part in balance1Parts)
            {
                balance1Part.HSway = decimal.Parse(values["HSway" + balance1Part.Order].ToString());
                balance1Part.SSpeeds = decimal.Parse(values["SSpeeds" + balance1Part.Order].ToString());
                balance1Part.LHSway = decimal.Parse(values["LHSway" + balance1Part.Order].ToString());
                balance1Part.RHSway = decimal.Parse(values["RHSway" + balance1Part.Order].ToString());
                balance1Part.PercentInLeftSphere = decimal.Parse(values["%InLSphere" + balance1Part.Order].ToString());
                balance1Part.PercentInRSphere = decimal.Parse(values["%InRSphere" + balance1Part.Order].ToString());
                balance1Part.TotalSway = decimal.Parse(values["TotalSway" + balance1Part.Order].ToString());
                balance1Part.ConvexHullArea = decimal.Parse(values["ConvexHullArea" + balance1Part.Order].ToString());
                balance1Part.Order = int.Parse(values["Order"].ToString());
                balance1.Parts.Add(balance1Part);
            }
        return balance1;
    }
}

I think the context isn't getting updated correctly for the parts as the second time I run this I would expect innerBalance1File to contain the parts but when I logged this out it was not there. Can anybody please advise what's wrong?

This is my context:

public class VRHContext : DbContext
    {
        public VRHContext(DbContextOptions<VRHitContext> options)
            : base(options)
        {

        }

        public DbSet<Organisation> Organisations { get; set; }
        public DbSet<ClientDeviceRegistration> ClientDeviceRegistrations { get; set; }

        public DbSet<Session> Sessions { get; set; }
        public DbSet<User> Users { get; set; }

        public DbSet<DataFile> DataFiles { get; set; }

        public DbSet<Symptoms> Symptoms { get; set; }
        public DbSet<Balance1> Balance1 { get; set; }
        public DbSet<Balance1Raw> Balance1Raw { get; set; }
        public DbSet<Balance2> Balance2 { get; set; }
        public DbSet<Balance2Raw> Balance2Raw { get; set; }
        public DbSet<Calibration> Calibration { get; set; }
        public DbSet<CogMotor1> CogMotor1 { get; set; }
        public DbSet<CogMotor1Raw> CogMotor1Raw { get; set; }
        public DbSet<CogMotor2> CogMotor2 { get; set; }
        public DbSet<CogMotor2Raw> CogMotor2Raw { get; set; }

        public DbSet<CogMotor3> CogMotor3 { get; set; }
        public DbSet<CogMotor3Raw> CogMotor3Raw { get; set; }

        public DbSet<Gait> Gait { get; set; }
        public DbSet<GaitRaw> GaitRaw { get; set; }

        public DbSet<Interception1> Interception1 { get; set; }
        public DbSet<Interception2> Interception2 { get; set; }
        public DbSet<InterceptionPlayerRaw> InterceptionPlayerRaw { get; set; }
        public DbSet<ManualDexterity> ManualDexterity { get; set; }
        public DbSet<ManualDexterityRaw> ManualDexterityRaw { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<User>().HasIndex(u => u.UserIdentifier).IsUnique();

            // Set default decimal precision.
            foreach (var property in modelBuilder.Model.GetEntityTypes()
                .SelectMany(t => t.GetProperties())
                .Where(p => p.ClrType == typeof(decimal) || p.ClrType == typeof(decimal?)))
                        {
                            property.SetColumnType("decimal(38, 10)");
                        }


            // Set default for GUID primary keys.
            foreach (var property in modelBuilder.Model.GetEntityTypes()
                .SelectMany(t => t.GetProperties())
                .Where(p => (p.ClrType == typeof(Guid) || p.ClrType == typeof(Guid?)) && p.IsPrimaryKey()))
            {
                property.SetDefaultValueSql("NEWID()");
            }
        }
    }

Some things I'm curious about. Should public DbSet<Balance1Part> Balance1Part { get; set; } be added to the context and should I have innerContext.Attach(Balance1Part); before innerContext.Entry(innerBalance1File).State = EntityState.Modified;?