What happens if I close a survey then reopen

I have a survey being delivered in 4 stages. The first two stages, I didn't close the survey, I just removed the url preview link from the facebook post to stop people accessing the survey, to allow me to update the piping logic for survey termination.

Prior to the third stage, I closed the survey access to allow me to work on the survey in case individuals had the survey tab open in their browsers and attempted to access while I was working on updating required changes. Which involved adding new additional questions to stage 1 & 2, plus adding on the stage 3 component.

The first three nights when stage 3 of the survey was running, no one complained of any issues. Then at lunch time today, people who were coming back to undertake stage 3 advised all their previous answers were gone. They mentioned they have not changed devices and I would like to know whether anyone has had similar instances of this occurring if they had closed the survey and then reopened.

Regards,

Jesse