[Bug]: Kwin 6.1.0 Switching workspace from empty workspace makes windows not show up

[sopyb]

Before you make the issue, confirm that

• You are running the master build from GitHub actions
• You have read the FAQ and the usage instructions
• You have searched pull requests and issues and have found none similar to your issue
• This problem comes from a failure in the tiling system and not a missing feature

Describe the bug

If I switch from a empty workspace into a workspace with a window on it the window (I assume) gets resized to 0x0 and I have to hit the toggle tiling hotkey I have to have the app showing again.

To reproduce

• Be on a empty workspace
• 3 finger gesture to move to another workspace with a window on it (also works with keybinds to a workspace or clicking in the workspace widget)
• Window is not visible not even when alt tabbing to it

Expected behavior

The window would show up and be tiled to the whole screen

Log output

no idea how to get those the page linked is empty

Screenshots and videos

No response

Additional context

No response

[sopyb]

2024-06-21.12-31-34.mp4

[alioth9]

I have quite the same bug except when I switch from an empty desktop to one with a window the window is still visible but move to point 0x0 and is under my top panel.
There is also a timing aspect: when I move from an empty VD to one with an app passing through a none empty one I could encounter the bug if I go fast but not if I pause between the desktop switch.
Beside some app are more prone to be affected than other. For example systemesettings is always affected but konsole or dolphin far less.
Also to describe what I see is that the windows are drawn to the correct size and position but then move to 0x0 and going under my top panel.

I just made a verification and It seems the bug don't happen if my top panel is not floating (in my default config I have a floating top panel).

Setup:
KDE Neon testing
plasma-desktop: 6.1.0

NB: initially I hesitate to post since I'm on kde neon testing but since sopyb post this and it seems quite similar than mine.
NB2: Thanks you so much for this good work on Polonium. Comming from awesome and sway I couldn't use kde/plasma without it.

[alioth9]

@sopyb did you encounter the bug if you change your panels configuration. unfloat, automatic hide. I think in particular your top panel

[sopyb]

I just checked it only happens when the panel is floating and always visible

[8uff3r]

I'm also having these problems on Fedora.

Making the panel non floating helps with windows disappearing but I still can't maximize windows and also toggling tiling make them disappear again

[sopyb]

I apparently upgraded to 6.1 without realizing 🤦 going back to a Nix generation on kwin 6.0.4 can't reproduce the bug there

[alioth9]

I can't maximize either but I in my case the windows don't disappear/are not resize. In the case of maximize, I can see that the windows try to maximize but seems to be prevented from it and goes back to the tiling.

[In-line]

Window Maximization is another KWin issue. Original change author just deleted unit test that would have prevented it :)

https://bugs.kde.org/show_bug.cgi?id=489463