Facets are missing post updating Apache Solr Search to 7.x-1.4 version
Just wanted to log the answer that is suggested on Drupal.org: https://drupal.org/node/2123683, since this question is the first thing that popped up when I ran into this issue.  :0)

Here is the issue: the taxonomy facets are the ones affected by the upgrade, because even though your taxonomy terms are probably hidden in the 'Search index' view mode on your content type's configuration page, apachesolr used to ignore those settings (a bug).

The new update fixes that, which means you need to go back to your content type's manage display page -> search index tab -> make sure the taxonomy terms in question are not hidden.

Hope this helps!