Bug 494386

SUMMARY
This was occurring on the latest 6.1.x and 6.2 update on Fedora, so I don't believe it was a regression from any update.

The visual bug is that it flickers between "full size" and "short/thick multi-row" which then hangs the plasma shell and causes major system lag, even causing screen flickering on tty sessions.

STEPS TO REPRODUCE
1. Panel is set to "Fit content"
2. Icon-only Task Manager is set to "Use Multi-row view: When panel is low on space and thick enough."
3. Log out/reboot system.
4. Log back into Plasma Desktop.

OBSERVED RESULT

The panel on start up expands to fill to the content on startup, which then counts itself as "low space, thick" and then attempts to draw rows and columns. It finishes the expansion, but still tries to use multi-row. This disagreement causes the panel to flicker between the two settings, hanging the shell/desktop in place. Krunner and other applications still function, you just can't dismiss notifications, use the panel's menu, or anything related with the panel's function.

Upon entering a tty session to attempt to debug, the tty session flickers between blank and the drawn terminal.

EXPECTED RESULT

The panel loads as normal, enabling full login and normal use.

SOFTWARE/OS VERSIONS

Operating System: Fedora Linux 40
KDE Plasma Version: 6.2.0
KDE Frameworks Version: 6.6.0
Qt Version: 6.7.2
Kernel Version: 6.10.12-200.fc40.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i5-8350U CPU @ 1.70GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620
[queue@wanderer]~% 


ADDITIONAL INFORMATION

After leaving the desktop alone while I was looking to see if this issue was a new issue or had a solution, it solved itself after a few minutes. I attempted to capture the panel flickering on video, but my phone couldn't see the rapid redrawing, I assume due to anti-banding. I have videos I can upload if needed.

If I had to guess (by observation, no dmesg/journalctl messages went off during this as far as I can tell), when this setting is enabled:
- The shell launches
- The panel launches
- It detects the setting is made to double up if its short and thick enough
- During the setting being detected, the panel is being drawn
- The panel being drawn is both short enough to stay one row, and thick enough to draw columns
- The two disagree, causing the panel to to rapidly draw between the two options, freezing the shell.