I can't think of anything changed in 2.20 that would affect this, but I really need a code sample to analyse it first.

Are you sure you can't put anything together that demonstrates the problem in a way you can share with me?

using Microsoft.Xrm.Sdk;
using Ploeh.AutoFixture;
using Ploeh.AutoFixture.AutoNSubstitute;
using Ploeh.AutoFixture.Xunit;
using Xunit;

namespace ClassLibrary3
{
public class NSubstituteCrmAutoData : AutoDataAttribute
{
/// <summary>
/// Initializes a new instance of the <see cref="Test" /> class.
/// </summary>
public NSubstituteCrmAutoData()
: base(
new Fixture().Customize(
new TestConventions(new CrmTestConventions(), new AutoNSubstituteCustomization())))
{
}
}

public class TestConventions : CompositeCustomization
{
/// <summary>
/// Initializes a new instance of the <see cref="TestConventions" /> class.
/// </summary>
/// <param name="crmTestConventions">
/// <see cref="CrmTestConventions" /> or a
/// derived implementation setting up conventions for the fixture.
/// </param>
/// <param name="autoMockCustomization">One of the AutoFixture automocking customizations.</param>
public TestConventions(
CrmTestConventions crmTestConventions,
ICustomization autoMockCustomization)
: base(
new OmitAutoPropertiesCustomization(),
crmTestConventions,
autoMockCustomization)
{
}

private class OmitAutoPropertiesCustomization : ICustomization
{
public void Customize(IFixture fixture)
{
fixture.OmitAutoProperties = true;
}
}
}

public class CrmTestConventions : ICustomization
{
/// <summary>
/// Customizes the specified fixture to return working <see cref="Entity" /> and <see cref="EntityReference" />objects.
/// </summary>
/// <param name="fixture">The fixture to customize.</param>
public virtual void Customize(IFixture fixture)
{
fixture.Customize<Entity>(f => f.WithAutoProperties().Without(e => e.ExtensionData));
fixture.Customize<EntityReference>(f => f.WithAutoProperties().Without(e => e.ExtensionData));

CustomizeSpecific(fixture);
}

/// <summary>
/// Override to register more specific default implementations for testing individual projects.
/// </summary>
/// <param name="fixture">The fixture to customize.</param>
protected virtual void CustomizeSpecific(IFixture fixture)
{
}
}

public interface IInterface
{
}

public class InterfaceImplemented : IInterface
{
}

public class FixtureX
{
[Theory, NSubstituteCrmAutoData]
public void Run_ExecutesUpdateEntityOnce([Frozen] IInterface intr, InterfaceImplemented sut)
{
// Arrange

// Act

// Assert
}
}
}