The check box with label "Use Solr" determines whether a search uses Solr.
If a search is set to use Solr (or has free text 2 Filters), then it MUST be populated after it has been saved:
Save the search → wait for the response, that the search was saved successfully → wait for the list of searches to reload → click the "cog wheel" → affirm that you want to populate the search. This creates a Job, which populates the Solr database. If everything is working as expected, the "cog wheel" SHOULD disappear from the list of searches.