Reproduced on https://demo.ametys.org/nightly-intranet-cms/www/index.html

But don't know exactly how !

I have created the link directory service on a new page. It worked.

I have added a new category and new links (without link text) in this category. 

The service didn't worked anymore. I have deleted some links (included the last created) and the service still didn't worked...

Local and nightly intranet errors logs attached.