Module SearchAdapterforSolr and Item Sets

I’m using an Omeka S 3.0.1 version, the latest version of Search (3.5.20.3) and SearchAdapterforSolr (3.5.24.3) modules and Apache Solr 8.8.2.

I am having a problem with facets for Item Sets while it works fine for items.

I have defined a resource template for Item Sets.

In Solr maps for “item_sets”, I have selected fields that are part of this resource model.

Ex. :
Source : level – Metadata to index : *_txt - level_txt
Source : dcterms:title – Metadata to index : *_txt – dcterms_title_txt

In the Search module configuration, I added a new index by entering the name (Default) and using the Solarium adapter.

I launched the indexing.

Then I created a Default page with search as path and Basic as form adapter.

In the configuration of the search page for core “default”, I selected these fields as facets (exept dcterms:title).

I created a custom navigation link to the search page and a page dedicated to the Solr search.

In the site settings and for Search module, I have selected Default(/search) as the default search page.

When I access the Solr search page on the site, I can see the facets associated with the fields specific to items, but for item sets, I can only see an “Item Set” facet in which the titles of the item set can be found (although this field has not been selected for the facets), but nothing for the other fields such as “level”, which I mentioned above.

When I query the indexes via the Solr administration interface, it finds nothing for the field “level”, for example, even though it was selected to be indexed.

Is it possible to have facets for fields specific to item sets and what about fields common to item sets and items ?