I am creating a directory using WordPress and I am having an issue with categories. I just created an importer using which I imported around 6,500 categories which are 3 level deep (parent -> child -> grandchild) and it looks like wp_list_categories isn't able to handle them well nor is the breadcrumb plugin provided by WordPress SEO plugin.
I would like to know if there are any special requirements to get WP to handle this number of categories? It works fine if I just import around 500 categories.
Please advice what the issue could be?