Hi @Henry,
Can you confirm what version of Survey123 field app you are using? Is it the latest 3.12?
Also, are you using Enterprise or ArcGIS Online? If it is Enterprise, what version and what type of authentication (IWA/SSO etc)? Also, do you use VPN and a MDM to manage the devices?
If the user is signed out unexpectantly, no data should be lost if the survey had already been saved to Drafts or Outbox. If the app was closed without saving, that may cause the survey to be lost. But once it is saved, ebing logged in or out has no impact on the saved surveys.
Regards,
Phil.