Why my publised survey changed all the time when I opened it?

Thank you for helping me! This is my survey Aircraft questions,but it changed all the time after I opened it. In this survey, I have three block, each of which has three questions, with a timer at the bottom of that block. For each block, only a question are randomly picked from three questions. When I preview my survey it works pretty well, but when I published and opened it, sometimes it just jump my first two block and directly ask the third block question. How come?