And just to be sure it wasn't my account since it had been updated/merged into the new plasma desktop I created a brand new user and the same issue persisted and desktop settings were not saved.

I am encountering this behaviour as well in 5.18.4 on Arch.

This seems to be contained to "Desktop Settings" only, as panel changes are saved, but it also occurs between login/logout for me as well.

Addition info....

What is odd about this is that the desktop layout settings are saved in ~/.config/plasma-org.kde.plasma.desktop-appletsrc but doesn't seem to be read at login.

Having the same issues on Arch as well (Plasma 5.8.15)
But with the difference that it doesn't happen to me on every login.
Haven't been able to figure any pattern as to why that happens to me.
In my case both the wallpaper and panels get reset, I'm using Latte dock and that one manages to save its settings.

(In reply to Carlos Santacruz from comment #4)
> Having the same issues on Arch as well (Plasma 5.8.15)
meant 5.18.5,

I have the same issue on Fedora 32.

Operating System: Fedora 32
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.13.2
Kernel Version: 5.6.14-300.fc32.x86_64
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-4300M CPU @ 2.60GHz
Memory: 7.5 GiB of RAM

plasma from this copr https://copr.fedorainfracloud.org/coprs/zawertun/kde/

I can workaround this issue by creating a script that copies a backup of the plasma-org.kde.plasma.desktop-appletsrc file back to the original on startup.

I had this issue since 5.18 came out.

To workaround this issue put this in ~/.config/autostart-scripts, after backing up ~/.config/plasma-org.kde.plasma.desktop-appletsrc to "~/.config/plasma-org.kde.plasma.desktop-appletsrc.g00d"

#!/bin/sh
sleep 25s
cp ~/.config/plasma-org.kde.plasma.desktop-appletsrc.g00d ~/.config/plasma-org.kde.plasma.desktop-appletsrc
killall plasmashell
sleep 1s
kstart5 plasmashell

I have this in KDE Neon 5.18.5 too. I've just experienced this in the last weeks, probably after updating to 5.18.4 or 5.18.5. It doesn't happen at every login, only once every 5 or 10 times. I haven't noticed a pattern yet.

In my case, all it does is:
- Change my desktop layout from "Desktop" to "Folder View".
- Change my desktop background from "Presentation" to "Image" (the 5.18 default one with the beach). And when I manually change it back to "Presentation", the default Plasma Wallpaper directory is present as the only source. I have to delete it and manually add my personal wallpaper folder.

This bug doesn't affect my panel at all. Fortunately, I can change my desktop back to my preferred configuration with a few clicks, so it's not a big deal time-wise. It's just a little annoying.

Observations on Manjaro, Intel HD 4000, Docking station/External Monitor:
1. Plasma on Xorg, Disconnected from Dock: Desktop settings loaded, ok
2. Plasma on Xorg, Boot connected to Dock: No Desktop settings, no panel, even on a fresh account
3. Plasma on Xorg, Boot disconnected from Dock, then connect: Desktop settings loaded and configurable via System settings/Monitor settings; ok
4. Plasma on Wayland (package plasma-wayland-session), Boot connected to Dock: Desktop settings loaded, ok

My experience is like David de Cos from comment #9.
This has happened twice to me (May and July 2020), 2 of about 8 restarts (all due to kernel updates). Both times my Plain Color wallpaper and Desktop layout revert to the default Fedora wallpaper and Folder View. But not every time; I set up debugging per https://community.kde.org/Solid/Projects/ScreenManagement#Debugging_Information before my last restart and my setup remained.

I have a laptop with external display that occasionally experiences a different Plasma wallpaper bug on startup, bug 422717.

SOFTWARE/OS VERSIONS
Operating System: Fedora 32
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.70.0
Qt Version: 5.14.2 (xcb)
Kernel Version: 5.7.9-200.fc32.x86_64
OS Type: 64-bit

Operating System: Manjaro Linux
KDE Plasma Version: 5.19.3
KDE Frameworks Version: 5.72.0
Qt Version: 5.15.0
Kernel Version: 4.19.133-1-MANJARO
OS Type: 64-bit
Processors: 4 × Intel® Core™ i5-7200U CPU @ 2.50GHz
Memory: 7.7 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 620

I'm having the same problem. I had it with the 5.7 kernel too, I changed it for other non related issues to the LTS. And also had this issue about 4 month ago.

Any plans to fix it?

I can confirm the issue in Kubutu 2020.04. I don't know which KDE version this is, for some reason it is missing from the About KDE dialogues.

Specifically keyboard shortcuts are not being saved. For instance, I removed the setting for Alt-F1 because the Jetbrains IDEs use this shortcut, but every time I log in I have to remove it again.

i created a bug report that obviously describes the same bug

forget about the first post - it DOES change the configuration.. it completely removes the "desktop containment" section and replaces it with the default "folder" section

https://bugs.kde.org/show_bug.cgi?id=423421

you can use my iso file in a virtualbox vm to recreate it - just reset is until you see it 

as others have already postet - it happens in 2 out of 10 cases .. completely random

I have a similar (but not identical) issue. Mine is that if you change the icon in a basic-link-to-folder, that gets reset.

I've already logged a separate bug for that. It's 429890 

My version is 
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8
Kernel Version: 5.4.0-52-generic

With my configuration (Kubuntu 20.10, KDE Plasma 5.19.5) the bug appears only in the specific  case an external monitor is attached. In this case my setting of Desktop Layout, Desktop, is always changed to Folder View.

*** This bug has been marked as a duplicate of bug 427861 ***