SUMMARY
When the window is moved so the right navigation panel is off the right edge of the screen, cursor hops lines, changed icon blinks.

STEPS TO REPRODUCE
... 
 if(foo) {
    bar;
  }
}

With cursor placed at the closing brace of the if-statement, it hops back and forth to the function closing brace. The line and column number at the bottom of the edit window follows the bouncing cursor, the file-changed icon in the tab title flashes. This nonsense stops as soon as I move kate's window leftward enough to reveal the navigation panel, but starts again as soon as the edit window navigation panel is just off the right edge of the screen or the edit changes are saved to disc.
(The window was moved to the right side of the screen to follow example code in the browser window on the left side of the screen.)

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
KDE Plasma Version: 5.20.4
KDE Frameworks Version: 5.77.0
Qt Version: 5.15.2
Kernel Version: 5.4.84
OS Type: 64-bit