Failure to export submissions to CSV

1. What is the problem? Be very detailed.
One of my forms failing to export data to CSV. I have 112 submissions for this form. On the server the data is encrypted and direct download from the server will give an unreadable CSV file. Also worrying, one of the 112 submissions went in unencrypted???

2. What app or server are you using and on what device and operating system? Include version numbers.
Server: ODK central server
Briefcase: ODK briefcase V1.18.0

3. What you have you tried to fix the problem?
Tried to download other forms using the same version of ODK briefcase and all worked fine. Tried to deleted the unencrypted record and failed.

4. What steps can we take to reproduce the problem?
Confused, stuck as well

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.