Summary says by itself. The problem occurs in plasma 5.14 beta on Arch Linux. Two user accounts are affected. My keyboard layout is brazilian portuguese (abnt2).
Can reproduce in Russian/Ukrainian layouts - on Wayland only Operating System: KDE neon Developer Edition KDE Plasma Version: 5.14.80 Qt Version: 5.11.1 KDE Frameworks Version: 5.51.0 Kernel Version: 4.15.0-34-generic OS Type: 64-bit Processors: 8 × Intel® Core™ i5-8250U CPU @ 1.60GHz Memory: 7,7 GiB of RAM
Tested both Arch and neon dev unstable running on different machines, same keyboard layouts. On Arch X11 task switcher does not show up. On Arch Wayland task switcher works as expected. On neon X11 task switcher works as expected. On neon Wayland task switcher shows up but it does not switch between the windows.
alt+' is working as expected on both Arch Linux (plasma 5.14.4) and neon dev unstable under X11 and Wayland sessions.