Hi Barry,
What version of the field app are you using? Is it 3.10?
Also on what devices (iOS or Android) with what OS version do you see this issue?
Not that several improvements were made to 3.10 release of field app to avoid unexpected sign out and better support for IWA SSO and other authentication types when both online and offline.
Is there any particular time or workflow that causes the sign out? A period of time, changing to offline, changing network from wifi to 4g to offline?
Regards,
Phil.