Is this on a Windows computer? If so, expired credentials may be stored in the Windows Credential Manager and need to be cleared- see https://community.esri.com/message/816736-re-cant-sign-in-with-survey123?commentID=816736#comment-78... . I would also recommend upgrading to the latest version of Survey123, as this issue was addressed in later releases.
Many thanks James. That fixed it!. I'm waiting for our organisation to package the latest version for release in our software centre so hopefully no more problems. Thanks for your time to have a look at this.