[Bug]: Several initial window position issues since Plasma 5.26

[karmux]

Summary

Bismuth worked for me flawlessy untill I updated Bismuth from 3.1.2 to 3.1.4 and Plasma from 5.25 to 5.26 yesterday.
There seem to be a new regression related to initial window positions with all apps.
I'm using super ultrawide monitor with tile layout and gap 10px between windows.

Firefox used to open in the center of the screen with correct gaps top and bottom. Now it opens with no gap at the top and double gap at the bottom. Firefox and Steam is not respected by other apps and they don't respect others - the can cover each other partially or completely. Minor gap problem also with System Settings when at least 2 windows are already open. Minimizing and unminimizing SS fixes the gap. Other apps seem to remember their last positions in the tiling. If I have some app (e.g Dolphin) open in the small bottom right tile and I close all windows and reopen only Dolphin then it opens in the same small tile.

Steps to Reproduce

Have Tile Layout and gap 10px between windows.

Firefox

1. Have no open windows
2. Open Firefox
3. Firefox opens in the center of the screen but have no gap at all at the top and double sized gap at the bottom

Firefox/Steam

1. Open Firefox or Steam
2. Open another random app A
3. Close Firefox or Steam and then random app A
4. Open again Firefox or Steam
5. It opens in the left side of the screen (wrong, related to "Weird positioning memory" issue described below)
6. Open any other app B which opens in the center of the screen not respecting Firefox or Steam and covers part of it.

System Settings

1. Open 2 random apps
2. Open System Settings
3. There is no gap between 2nd app and System Settings. Minimizing and unminimizing SS fixes gap problem.

Weird positioning memory

1. Open 2 random apps
2. Open 3rd random app
3. Close all apps in order: 3rd, 2nd, 1st
   4.Open 3rd app again which opens at the same position it was closed

Expected behavior

Firefox: Firefox should open having 10px gap top and bottom

Firefox/Steam: All apps must respect Firefox or Steam and not cover them.

System Settings: There must be 10px gap between SS and app opened before it.

Weird positioning memory: First app should open in the center of the screen not in the corner where it was last time when many windows were open.

Screenshots

No response

Bismuth version

3.1.4

KDE Plasma version

5.26.2

The platform KWin is running on

X11

Additional context

No response

[CarlosEkisde]

This is probably the same bug as #421