Search not finding TablePress content

Relevanssi expands shortcodes in the post content, including the TablePress shortcodes. Looking at the HTML source code of your page, the tables are inside page builder modules. That’s probably the cause of the problem – if the TablePress shortcodes are not in the post content, they’re harder to use.

If you create a new page without any page builder features and just place a TablePress shortcode in the post content and then save the page, can Relevanssi find that page when you search for the table contents?

Likely yes. Are the shortcodes contained in post content, or in custom fields?

Can you show me how that post looks like in the wp_posts database table?

Yes, that. The post_content is completely empty there, so the post content is stored somewhere else. Likely in custom fields, and Relevanssi does not expand TablePress shortcodes in the custom fields.

You can try adding this to your theme functions.php:

add_filter( 'relevanssi_custom_field_value', 'rlv_tablepress_in_custom_fields' );
function rlv_tablepress_in_custom_fields( $contents ) {
	$tablepress_controller = relevanssi_enable_tablepress_shortcodes();
	relevanssi_disable_shortcodes();
	$contents = do_shortcode( $contents );
	unset( $tablepress_controller );
	return $contents;
}

Add this and rebuild the index.

Sure. All I know of Oxygen is that it goes pretty far from regular WordPress stuff, and it’s quite likely it’s just not possible make this work.