Created attachment 156287 [details]
Screenshot

SUMMARY
Under some circumstances, when Kate would have to load a tab in another split view that hasn't been active since Kate was started (which can happen if the tab comes from a saved session), it fails to load the editor component. See screenshot.

STEPS TO REPRODUCE
1. Start Kate with a new session.
2. Open File A.
3. Click Split Vertical. Now file A is open on both sides, and the right side is focused.
4. Open File B.
5. Click in the editor on the left side to focus it.
6. Open File B there too.
7. Click the tab with File A on the right side split to activate and focus it.
8. Save the session.
9. Close Kate.
10. Open Kate again, and open the session just created. A and B are open on both sides, B is active on the left side, A on the right side, and the right side has keyboard focus.
11. Click in the editor on the left side to focus it.
12. Close Tab A on the right side with the X button.

OBSERVED RESULT
On the right side,, Kate switches to Tab B, but it fails to load the katepart, resulting in an empty area where the editor should be. (See screenshot.)

EXPECTED RESULT
The editor on the right side view is loaded.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20230214
KDE Plasma Version: 5.27.0
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8
Graphics Platform: X11

ADDITIONAL INFORMATION
Might be related to Bug 465807 or Bug 465808. In many circumstances (such as if you skip Step 6, so B is not opened on the left side), Bug 465808 occurs too, i.e. Kate switches to a different file on the focused side. (Katepart is loaded correctly there.)