SUMMARY

Some terms I used:
- unsaved document: a new Kate editor tab with some text content, that the user did not explicitely save into a file on the filesystem
- preserve: Kate saving the document's unsaved parts to an internal directory

Lets assume that the following settings are enabled:
- Open/Save > Advanced > Swap file mode: Enabled, Store In Default Directory
- Session > Application Startup/Shutdown Behavior > Automatically save and restore: Newly-created unsaved files

If the user creates a new document or more, writes something in it, but does not save it to a file in the filesystem (because they intend it as a temporary note or something of that sort), Kate does not try to preserve it for when a crash might happen.

STEPS TO REPRODUCE
1. Open Kate, load a saved session
2. Create new documents, write something into them
3. Make the system crash, or simulate a crash with SIGKILL to Kate
4. On next boot, open the Kate session used in step 1
5. Find the unsaved documents in the "Documents" side panel on the left, and open them

OBSERVED RESULT

The opened, unsaved documents are empty.

EXPECTED RESULT

The opened, unsaved documents should preserve their content from before the crash.
This is already what happens if Kate is closed gracefully, even if the user did not explicitly save the session in the "Sessions" toolbar menu.

SOFTWARE/OS VERSIONS
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: openSUSE Leap 15.6
KDE Plasma Version: 5.27.11
KDE Frameworks Version: 5.115.0
Qt Version: 5.15.12

ADDITIONAL INFORMATION

It seems Kate already preserves these unsaved files to some extent, as even after a crash they will appear as files in the Documents panel, with names like "Untitled", "Untitled (1)" and so on.