Wrong back-end language
When Multi-language mode in the SobiPro is disabled and in the Joomla! configuration is used other language on the front-end than in the back-end, then in the SobiPro back-end is used front-end selected language. So for example, if I set in Joomla! to use PL in front and EN in back-end then SobiPro back-end use PL language.