After upgrading from .NetFramework with EF to .Net8 with EFCore I am unable to modify my SalesQuotes.

I am using Table Per Type.

The following code fails

        var connect = HandyDefaults.MakeConnectFromConnectionString(connectionString);
        var quote = connect.SalesQuotes.SingleOrDefault(x => x.DocumentNumber == "SQ000017");
        var guidString = Guid.NewGuid().ToString();
        quote.CustomerReference = guidString;
        connect.SaveChanges();
        connect = HandyDefaults.MakeConnectFromConnectionString(connectionString);
        var quote2 = connect.SalesQuotes.SingleOrDefault(x => x.DocumentNumber == "SQ000017");
        Assert.AreEqual(guidString, quote2.CustomerReference); // fails

Where the DbContext is constructed

    public static MyEFCoreDbContext MakeConnectFromConnectionString(string connectionString)
    {
         
        var optionsBuilder = new DbContextOptionsBuilder<MyEFCoreDbContext>()
          .UseSqlServer(connectionString)
            .UseChangeTrackingProxies()
            .UseObjectSpaceLinkProxies();
        return new MyEFCoreDbContext(optionsBuilder.Options);
    }

And in OnModelCreating I have

modelBuilder.SetOneToManyAssociationDeleteBehavior(DeleteBehavior.SetNull, DeleteBehavior.Cascade);
modelBuilder.HasChangeTrackingStrategy(ChangeTrackingStrategy.ChangingAndChangedNotificationsWithOriginalValues);
modelBuilder.UsePropertyAccessMode(PropertyAccessMode.PreferFieldDuringConstruction);

as well as

    modelBuilder.Entity<SalesQuoteLine>()
        .HasOne(j => j.SalesQuote)
        .WithMany(x => x.Lines)
        .HasForeignKey(x => x.SalesQuote_Id)
        .OnDelete(DeleteBehavior.Cascade);

The business model is something like

public class SalesQuote : BaseSalesHeader
public SalesQuote(){
       Lines = new ObservableCollection<SalesQuoteLine>();
                   }
       public virtual ObservableCollection<SalesQuoteLine> Lines { get; set; }
       // other properties
}

With BaseSalesHeader similar to

public abstract class BaseSalesHeader {}  // contains properties common to different sales documents.

I am using EntityFrameworkCore 8.01, .net8 , C#, SQLServer

I am able to add Sales Quotes but not modify.