I found an issue that may be the one you have: in newer versions or in some configs of Solr, there is no default field by default, so the default query returns nothing, because it searches nowhere. I’ll publish a new version soon to add it automatically in the default mapping.
As a quick workaround, you can add the default field _text_ with * as source, then run a indexation:
See the Solr guide about catchall copy field.
What is your solr version? Is it fixing it?