When generating search results, the Yandex search algorithm tries to take into account the user's interests.
If you can't disable search suggestions, your browser probably doesn't save cookies, so settings aren't saved either. As a result, your current interests will be taken into account again after a certain period of time.
Make sure that cookies are enabled in your browser (in the browser settings). If cookies are enabled, but personalized search settings still aren't being saved, then the problem is with the browser itself. Contact its support service.