"previous" button dissapeared

Hi!
I use Pavlovia Surveys and have many pages with simple questions. In “Navigation” section of General settings I turned on “Show the Previous Page button”. In preview mode I see this button (previous), but in live mode (when I use link to the survey) this button doesn’t exist (I see only “next” button). And this happens not only with new survey, but with old surveys too (the “previous” button dissapeared). In December all worked as needed (“previous” button was shown in live link). Could you please help me understand how can I allow respondents go back to previous questions?