VS 2017 Designer: Method not found - visual-studio-2017

Question

I have a windows form that contains a user control (each defined in separate assemblies). Both the form and the user control call an extension method on BindingList<>. The extension method is defined in a 3rd assembly. Everything compiles & runs fine.
However, if I try to open the form in Visual Studio 2017 designer, I get an error:
To prevent possible data loss before loading the designer, the following errors must be resolved:
Method not found: 'System.ComponentModel.BindingList1 KamaTrenda.Utilities.Lists.ListUtilities.AddReset(System.ComponentModel.BindingList1,
System.Collections.Generic.IEnumerable`1)'.
Call stack:
at System.ComponentModel.ReflectPropertyDescriptor.SetValue(Object
component, Object value) at
Microsoft.VisualStudio.Shell.Design.VsTargetFrameworkPropertyDescriptor.SetValue(Object
component, Object value) at
System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializePropertyAssignStatement(IDesignerSerializationManager
manager, CodeAssignStatement statement,
CodePropertyReferenceExpression propertyReferenceEx, Boolean
reportError) at
System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeAssignStatement(IDesignerSerializationManager
manager, CodeAssignStatement statement) at
System.ComponentModel.Design.Serialization.CodeDomSerializerBase.DeserializeStatement(IDesignerSerializationManager
manager, CodeStatement statement)
Commenting out the content of the setter of this property allows for opening the form in the designer:
public IList<IPosition> PositionsToDisplay
{
get { return myPositionsToDisplay.Select(x => x.Position).ToList(); }
set { myPositionsToDisplay.AddReset(value.Select(x => new PositionAdapter(x))); }
}
myPositionsToDisplay:
private readonly BindingList<PositionAdapter> myPositionsToDisplay = new SortableBindingList<PositionAdapter>();
And AddReset:
public static class ListUtilities
{
public static BindingList<T> AddReset<T>(this BindingList<T> list, IEnumerable<T> toAdd)
{
list.RaiseListChangedEvents = false;
foreach (T item in toAdd)
list.Add(item);
list.RaiseListChangedEvents = true;
list.ResetBindings();
return list; // for chaining
}
}
I have tried adding
[Browsable(false), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
to the definition of PositionsToDisplay, and it made no difference.
I tried rebuilding, manually deleting the contents obj & bin directories for all 3 projects, as well as the contents of AppData\Local\Microsoft\VisualStudio\15.0_6d397e1a\ProjectAssemblies, closing all open documents in VS 2017, closing the solution, and restarting Visual Studio, and it made no difference.
The .resx file of neither the form, nor the control, refer to the property.

Answer 1

The Designer.cs for the form had some code that seemed to be causing the issue:
this.control.PositionsToDisplay = ((System.Collections.Generic.IList<IPosition>)(resources.GetObject("control.PositionsToDisplay")));
Deleting this (presumably after adding DesignerSerializationVisibility.Hidden, so that it does not get re-generated) seemed to solve the issue.