SUMMARY
If you use saved sessions and split views, and quit Kate while the "Hide Inactive Views" mode is active, and then reopen Kate, the other split views are forgotten, as if they had been closed completely, rather than just hidden.

The list of open files is preserved though, so files that were only open in a hidden split view remain available in the Documents plugin and in the Ctrl+Tab switcher

Additionally, if there was only one tab in the visible view (and thus after reopening Kate), then the katepart menu and toolbar items are not loaded when reopening Kate.

STEPS TO REPRODUCE
1. Open a saved session.
2. Click Split Vertical (if you don't have split views already).
3. Click Hide Inactive Views. Optionally, open some documents in each view.
4. Quit Kate.
5. Open Kate again with the same session.

OBSERVED RESULT
The Hide Inactive Views action is inactive and disabled, as when there is only one view. The Split Vertical and Split Horizontal actions are enabled.

If, at this point, there is only one visible tab, actions provided by katepart are missing from the menus and the toolbar, albeit the file is visible and can be edited.

EXPECTED RESULT
The Hide Inactive Views action is enabled and active. The Split actions are disabled, as when Hide Inactive Views is enabled. Clicking Hide Inactive Views inactivates it, and the other split view(s) are there again. The katepart actions are available.

Even if saving the Hide Inactive Views state in sessions isn't implemented, I'd expect all split views to be remembered, rather than just the one that was visible before quitting.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20230527
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9
Kernel Version: 6.3.1-2-default (64-bit)
Graphics Platform: X11