I'm running 1.70+ (build 4690). Although we tested our survey in house with no errors before releasing it, we've now got several survey users reporting similar errors. In speaking to several of the users, the errors seem to be produced when they use the "prev" button during the survey.
The error they're getting:
"An unexpected error has occurred and your responses cannot be saved.
Your responses have not been lost and have been emailed to the survey administrator and will be entered into our database at a later point."
We're receiving "Error saving results" emails that correspond to users getting the error above. The good news is that their data actually *was* saved as an incomplete response, so it's not lost. However, users report that they get the same error when they attempt to access the survey again.
Is this a known bug that was fixed in later releases? I've been reading release notes and searching the forum with variations on the error text and haven't found anything definitive yet.
BUT, having done those forum searches (and having gotten the security advisory email over the weekend about upgrading), I'm guessing the recommendation in any case will be to upgrade to the newest release

Which I'm happy to do, but I just want to confirm -- is it safe to do that while running an active survey? Will it in any way impact users who saved their surveys to continue later? Relatedly, we have the token persistence feature on -- will upgrading impact a user's ability to pick up where they left off?
Thanks very much in advance for any assistance!