catalog_category_product_index table empty (Magento 2.2.5)

Our indexer re-fills the table catalog_category_product_index_store1, but the table catalog_category_product_index remains empty.

I have found this issue https://github.com/Smile-SA/elasticsuite/issues/991 , but even after an upgrade of the smile/elasticsuite module to 2.5.13, the table remains empty.

In some of our development environments, the table is filled. But when I truncate it and reindex, it stays empty.

This is how I reindex:

bin/magento indexer:reindex catalog_product_category 

Any ideas?