A Managed Solr user asked for help when his collection contained data but queries came back empty.
In this instance it turned out that the user had forgotten to commit the index before querying. This is a common experience when users are loading and querying for the first time.
$ curl -X POST -H 'Content-type:application/json' -d <datafile> '<Solr HTTP Endpoint><collectionName>/update?commit=true'
Be careful with commits!
The advice on this page skirts the most-common new-user mistake with Solr: performing commits too frequently.
See Timeouts during ingestion: Too many commits! for a discussion of this important topic.