First: This might be the wrong product. It was the least inappropriate keyboard-related product I could find.

I made a big system update to my ARCH/KDE linux system on 2019-07-17, which updated, among others, plasma from 5.16.2 to 5.16.3, and kde-frameworks from 5.59.0 to 5.60.0. After that, the dead keys on my keyboard layout stopped working. Now, they do nothing at all, as if the keyboard was broken (except for shift-^, which is not dead IIRC).

I tried to downgrade some packages (kwin, khotkeys, plasma-framework, plasma-workspace, kglobalaccel, kded, xorg-setkbmap, systemsettings), but it didn't help.

Funnily enough, in gtk-based software (e.g. Firefox), these keys work just fine, even in the same session.

Steps to reproduce:
1. Switch to the default german layout in ksystemsettings
2. Open some kde application where you can write text (e.g. kwrite)
3. Press the ^ key and then space
4. Press the the accent key (any keyboard layer you like) and then space

Expected:
Writes "^" and whatever accent you chose in step 4

Actual:
Writes "  " (two spaces)

SOFTWARE/OS VERSIONS
Linux Kernel: 5.2.2-arch1-1-ARCH
KDE Plasma Version: 5.16.2
KDE Frameworks Version: 5.60.0
Qt Version: 5.13.0