PHP warning in admin area

Thanks for reporting this, it looks like there was an issue with a string in the Russian translation. I have fixed it in GlotPress and you can grab the updated .mo file from here: https://github.com/mtekk/Breadcrumb-NavXT/blob/master/languages/breadcrumb-navxt-ru_RU.mo?raw=true

Download the updated .mo file and then replace the old file, with the same name, on your server (should be under WPCONTENT_DIR/plugins/breadcrumb-navxt/languages, where WPCONTENT_DIR is the location of your wp-content directory).

Thank you very much! It helped me.