The integrated plugin update from 2.1.4 to 2.2.0 failed. It complained because the wp_content/plugins/crayon-syntax-highlighter folder already existed. Now I see neither the old nor the new version of the plugin listed. The crayon-syntax-highlighter folder is still there (has a few subfolders but no PHP files) but the plugin is somehow gone. No more highlighting.
Had to manually FTP the files to the server and activate the plugin again.