Version 1.13.3 mostly fixes an undefined variable error that can come up when saving posts. Other changes are mostly minor fixes, either small bug fixes that affect edge cases and only a small percentage of users. However, that undefined variable error is so common that the update is recommended for all users.
relevanssi_display_common_wordscan be used to disable the “25 most common words” listing on the settings page, if it’s too heavy to load.
relevanssi_do_not_indexfilter caused error messages.
relevanssi_post_title_before_tokenizefilter now has a second parameter that contains the post object.
post_parent__not_in, though you have to set them in
relevanssi_modify_wp_queryfilter for them to work.