Created attachment 143517 [details]
Backtrace of this crash, missing many symbols.

SUMMARY
***
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***
When I run System Monitor, type a process name filter, and close a large number of processes matching the filter, switching to tree view produces QML errors and sometimes segfaults.

STEPS TO REPRODUCE
1. Open plasma-systemmonitor to the Processes tab.
2. Optionally switch to tree view.
3. Type bash into the search bar.
4. Open a Konsole tab, open Bash if you're using a different shell, and run `for i in {1..200}; do bash & done`.
5. Once the 200 bash processes show up in plasma-systemmonitor, close the Konsole tab, and wait for the processes to disappear.
6. Switch to tree view if you're not already in it. Warnings will not appear unless/until you're in tree view.

Without a search query open, I don't get instability (fixed in Bug 437862).

If you run a different child process (like perl), you can encounter this bug by searching for perl instead of bash. And if you start out in list view and later switch to tree view, you can *only* reproduce the bug by searching for perl (not the parent process bash).

OBSERVED RESULT

```
TableView::forceLayout(): Cannot do an immediate re-layout during an ongoing layout!
Model size of -1 is less than 0
Model size of -1 is less than 0
Model size of -1 is less than 0
...
file:///usr/lib/qt/qml/org/kde/ksysguard/table/TreeDecoration.qml:49: TypeError: Value is undefined and could not be converted to an object
file:///usr/lib/qt/qml/org/kde/ksysguard/table/FirstCellDelegate.qml:57:42: Unable to assign [undefined] to bool
file:///usr/lib/qt/qml/org/kde/ksysguard/table/FirstCellDelegate.qml:56:44: Unable to assign [undefined] to bool
file:///usr/lib/qt/qml/org/kde/ksysguard/table/FirstCellDelegate.qml:55:39: Unable to assign [undefined] to int
file:///usr/lib/qt/qml/org/kde/ksysguard/table/TreeDecoration.qml:49: TypeError: Value is undefined and could not be converted to an object
file:///usr/lib/qt/qml/org/kde/ksysguard/table/FirstCellDelegate.qml:57:42: Unable to assign [undefined] to bool
file:///usr/lib/qt/qml/org/kde/ksysguard/table/FirstCellDelegate.qml:56:44: Unable to assign [undefined] to bool
file:///usr/lib/qt/qml/org/kde/ksysguard/table/FirstCellDelegate.qml:55:39: Unable to assign [undefined] to int
,,,
```

In some rare cases I get a crash as well. For example, when filtering in plasma-systemmonitor, I got a crash "in the wild" a few days ago with a non-symboled backtrace (attached), but it's missing the actual coredump. Since then, I've only been able to replicate this crash in synthetic conditions using non-symboled Arch Linux plasma-systemmonitor in painfully-slow Valgrind (my (!strip debug) builds don't crash).

EXPECTED RESULT
plasma-systemmonitor doesn't crash and doesn't use invalid object indexes.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.23.3
KDE Frameworks Version: 5.87.0
Qt Version: 5.15.2
Kernel Version: 5.14.16-zen1-1-zen (64-bit)
Graphics Platform: X11
Processors: 12 × AMD Ryzen 5 5600X 6-Core Processor
Memory: 15.5 GiB of RAM
Graphics Processor: NVIDIA GeForce GT 730/PCIe/SSE2

ADDITIONAL INFORMATION