Search API + Apache SOLR - No highlighted excerpts returned for stemmed terms
I'm guessing that you, like me, had the "Highlight" filter enabled, which you shouldn't actually do for Solr. I found this nugget of info here:

https://www.drupal.org/node/2358065#comment-9319765

Though Solr returns the excerpt, that processor removes it if there's not an exact match.