Hello,
I am running Arch LTS with KDE Plasma and a dual monitor setup (plasma-desktop 5.26.1-1, breeze 5.26.1-1). My issues started after upgrading to the latest plasma-desktop (5.26.1-1). After waking the PC from sleep, one of the monitors just wouldn't connect, even though it showed up on Display Configuration in System Settings. I tried the usual trick of editing the "plasma-org.kde.plasma.desktop-appletsrc" file and setting lastScreen=0. It didn't work. Then, like a crazed animal, I tried the following:

1) Deleted plasma-org.kde.plasma.desktop-appletsrc and restarted PC, hoping it would mend itself. It didn't. On the contrary the taskbar icons became huge and I lost all formatting.
2) Uninstalled plasma desktop and reinstalled it. No effect.
3) Removed plasma-org.kde.plasma.desktop-appletsrc, plasmashellrc, and everything under /usr/share/plasma. Then uninstalled and reinstalled plasma-desktop. No effect!

After hundreds of random but hopeful clicks on various settings I have somehow managed to get both monitors working. They are still touch an go however - if the screens enter power save mode due to inactivity, I have to revive one monitor from Display Configuration. I have two big questions:

1) What can I do to ensure the dual monitor setup works without breaking every time the screens enter power save mode (I still dare not put the PC to sleep!).
2) I have lost all visual effects/formatting on the taskbar. E.g. The application icons are huge and there is no spacing between them. If an application is open I can tell if it is (previously the icon would be highlighted). The "start menu" (apologies for using Windows terminology here, it's blasphemy I know!) has no padding. everything looks really ugly. The settings under "Configure Icons-only Task Manager" or "Edit Mode" have no effect whatsoever.

As you can tell from the above I don't mind tinkering. It is however mindless tinkering because I don't know what I'm doing. I am eager to learn. Please help by pointing me in the right direction.
Many thanks,
KT.