Relevanssi doesn’t work with the WP Job Manager search. The solution is fortunately simple: you can just disable Relevanssi for the WP Job Manager page.
To disable Relevanssi, add this to your site:
add_action( 'get_job_listings_init', 'relevanssi_fix_for_wp_job_manager' );
function relevanssi_fix_for_wp_job_manager(){
remove_filter( 'posts_request', 'relevanssi_prevent_default_request' );
remove_filter( 'the_posts', 'relevanssi_query' );
}Thanks to Adam Lenz for this solution.