The problem is also only occurring for some, not for all participants. When I test it, I can't replicate the error.
OK, so this shouldn't be a problem with your installation then, if it works for you and if it works for most of them.
Maybe it's because of some settings with their devices or browsers?
At least the response persistance setting should not be impacted by their device, because it is basically a purely server side function. The responeses are saved on the server and the same link should open where they hade stopped.
However, how is your survey displayed? I am wondering if all questions are on the same page? In this case, nothing has been stored. The responses are only saved if you click on a button "next" or "submit". For all in one surveys there is no such button clicked until you submit the survey. But, this also can't be, if it works for you.