Sometimes, the Spellchecker (or "Did you mean?") feature powered by Solr may not be working as expected. Under those cases, you may attempt to issue a forced rebuild of the spellchecker dictionary by issuing an API call to Solr. The drush snippet below should trigger this operation.
Note that, given the high-availability nature of Acquia Search Solr, it may take up to 5 minutes for the spellchecker to be generally available for all search queries, while replication between the Solr backends happen.