Profile: Support

The problem was in TLC1.2
Read this topic
https://stackoverflow.com/questions/34920429/is-tls-1-1-and-tls-1-2-enabled-by-default-for-net-4-5-and-net-4-5-1

You didn't enable TLC1.2 for nop store.
I did it in new release of plugin.  Download the new one and try it.
Write me about result.

Please check if this product Product A1.1 (and this Product A1.2  too )is in another category in one time (ex. in several catogories).

Write me I wait.

Please check it again.
Maybe you saw the feed file from browser's cache.

  <FeedAttribute>
    <Id>31</Id>
    <FeedCaption>Custom label for Shopping Campaigns 0</FeedCaption>
    <FeedName>custom_label_0</FeedName>
    <FieldNameCode>productcost</FieldNameCode>
    <ConvertValues />
    <CharsLimit>100</CharsLimit>
    <Required>false</Required>
    <IgnoreNullOrEmpty>false</IgnoreNullOrEmpty>
    <UseCDATA>false</UseCDATA>
    <ActionId>0</ActionId>
    <AdvancedField>true</AdvancedField>
    <RowSourceType>0</RowSourceType>
    <AttributeControlType>0</AttributeControlType>
  </FeedAttribute>

ID is unique key for each field.
Change it with value 45645654 and try.

Check if you has
<Id>51</Id>
only one time.
Maybe you copy existing ID and this template has two items with ID 51

Why didn't you use the city for billing address?
You use only city for shipping address.
Example

"billing_address":{"country_code":"IT","postal_code":"20101","state":"MI"}}
"shipping_address":{"recipient_name":" ","city":"Milano","country_code":"IT","postal_code":"20101","state":"MI"}

Thank you too.
Please write a review about our support
https://www.nopcommerce.com/p/2707/tracking-code-manager-facebook-pixel-google-tag-manager-tradetracker-etc-foxnetsoftcom.aspx

I need to think.

You are right.
I have found the bug and solved it.
Download new ZIP file and replace DLL file. Restart your nop store and try.
Write me about result.