The title field in search results using the SOLR endpoint seems to always be null. For example, making a request to
returns a result like:
Looking at the code a bit, it looks like it's trying to populate the title from the "title" field in the solr document. However this field seems to be a multi-lingual field, so it should probably look in the appropriate localized field, e.g. "title_en". I have a PR incoming to fix this.