Move from 1.8.3 to 2.1.7 - why a shape that work before never work anymore?

[PiemP]

Probably is a bad use of code. I call a shape in this way:

...
<shape type="info__footer" alias="alias:footer-columns" cache-id="info-footer" cache_tag="alias:footer-columns" />
...

in Info-Footer.liquid I retrieve the content item and call this code:

{% assign my_content = Content[Model.Properties.Alias] %}

{% if my_content != null %}
  {{ my_content | shape_build_display: "Detail" | shape_render }}
{% endif %}

In OC 2.1.7 the display of the content item shape give me this exception:

Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware|ERROR|An unhandled exception has occurred while executing the request. System.NotImplementedException: The method or operation is not implemented.
   at OrchardCore.DisplayManagement.PositionWrapper.get_Items()
   at ItemsGetter(Object)
   at System.Text.Json.Serialization.Metadata.JsonPropertyInfo`1.GetMemberAndWriteJson(Object obj, WriteStack& state, Utf8JsonWriter writer)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryWrite(Utf8JsonWriter writer, T value, JsonSerializerOptions options, WriteStack& state)
   at System.Text.Json.Serialization.JsonConverter`1.TryWrite(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)
...

The content item loaded by Content[Model.Properties.Alias] contains a BagPart (named Columns) that contains other content items that have a FlowPart.

If I call directly in Info-Footer.liquid the code in content item Detail shape the exception is never throw.

The Detail shape code is this:

{% if Model.ContentItem.Content.Columns.ContentItems.size > 0 %}
<div class="row">
  {% assign colsize= 12 | divided_by: Model.ContentItem.Content.Columns.ContentItems.size %}
  {% for item in Model.ContentItem.Content.Columns.ContentItems %}
    <div class="col-md-{{ colsize }} pb-2">  
    {% for item in item.FlowPart.Widgets %}
      {{ item | shape_build_display: "Summary" | shape_render }}
    {% endfor %}
    </div>
  {% endfor %}
</div>
{% endif %} 

Why this code never work anymore? What I miss?
Thank you.