All Samsung Devices with the Knox email app.
This issue occurs with the following chain of events.
1. An email is composed in the Knox email app.
2. The Device loses network connectivity.
3. The Knox Workspace container is locked.
4. The device network connectivity is restored.
5. An Email is sent in the background with the Knox Workspace locked, but the email body is missing.
This issue occurs because when the Knox Workspace is locked, the data is protected by the Sensitive Data Protection(SDP) feature which prevents any data leaks.
Workaround - Send emails only when the Knox Workspace is unlocked.