Hi,
If the content is not searchable, it usually means it’s dynamically generated, and not directly stored in the database. For example using shortcodes only as content. For that, there is a secondary, index table engine, which was built for cases like this. It makes an index of keywords based on visible post content (if possible). Please check these documentation links:
– Index table introduction
– Configuring and Generating the index table
The custom fields are printed by default, due to their possibly extremely large numbers. There is a search field above the custom fields option to look for custom fields: http://i.imgur.com/vgYXnZd.png
When clicking the Search all custom fields? option the area greys out to indicate that the option below is no longer effective, because all custom fields are used anyways – no matter which ones are selected.