SetProperty throwing InvalidCastException

[GillesBer]

I have a recent problem on my CSLA object, that I can't figure out.
This app uses CSLA 4.11 (sic), and defines one of its properties what I believe is/was the 'standard way':

` public static readonly PropertyInfo ActionPlanProperty = RegisterProperty((c) => c.ActionPlan, "Action Plan");

	public Actions ActionPlan
	{
		get
		{
			if (!FieldManager.FieldExists(ActionPlanProperty))
			{
				LoadProperty(ActionPlanProperty, Actions.NewActions());
			}
			return GetProperty(ActionPlanProperty);
		}
		set
		{
			SetProperty(ActionPlanProperty, value);
		}
	}

`

With NewActions defined as:
public static Actions NewActions() { return DataPortal.CreateChild<Actions>(); }

When I use the property setter for the first time, I get an exception from this CSLA code:

https://github.com/MarimerLLC/csla/blob/main/Source/Csla/Core/BusinessBase.cs
which used to be:
protected void SetProperty<P>(PropertyInfo<P> propertyInfo, P newValue, Security.NoAccessBehavior noAccess) {
//...
//=> The type returned in fieldData is not the one I was expecting (FieldData)
var fieldData = FieldManager.GetFieldData(propertyInfo); if (fieldData == null) {
//...
} else { var fd = fieldData as FieldManager.IFieldData<P>; if (fd != null) oldValue = fd.Value; else
//=> Here I got an InvalidCastException : 'Unable to cast object of type 'System.Int32' to type 'MyNamespace.Actions'.'
oldValue = (P)fieldData.Value;

I suspect the cause is around ((IPropertyInfo) propertyInfo).Index which (I think) incorrectly returns the index "1" . At this index, the FieldManager._fieldData contains another Property of my class which is of type PropertyInfo<int> instead of my PropertyInfo<Actions>; thus the InvalidCastException.
I'm trying to understand what causes the issue, but I don't know where/how to troubleshoot further.
I'm able to add breackpoints in the CSLA source code if I know where to look.

Thanks for your guidance!