SUMMARY
Clicking on the launcher and pressing tab key will freeze plasmashell consistently.

STEPS TO REPRODUCE
1. Click the lanucher
2. Press TAB
3. No 3rd step

OBSERVED RESULT
Plasmashell freezes with 100% CPU

EXPECTED RESULT
Nothing happens

SOFTWARE/OS VERSIONS
Windows: 
MacOS: 
Linux/KDE Plasma: Arch Linux
(available in About System)
KDE Plasma Version: 5.14.5
KDE Frameworks Version: 5.54
Qt Version: 5.12.0

ADDITIONAL INFORMATION
Happens on 2 different systems.

Perf Report for plasmashell when issue happens.

# Overhead  Command      Shared Object          Symbol                                            
# ........  ...........  .....................  ..................................................
#
    26.71%  plasmashell  libQt5Quick.so.5.12.0  [.] 0x0000000000206be8
    22.16%  plasmashell  libQt5Quick.so.5.12.0  [.] 0x000000000020679e
    11.09%  plasmashell  libQt5Quick.so.5.12.0  [.] 0x0000000000206793
     9.04%  plasmashell  libQt5Quick.so.5.12.0  [.] QQuickItemPrivate::nextPrevItemInTabFocusChain
     6.46%  plasmashell  libQt5Quick.so.5.12.0  [.] QQuickItemPrivate::nextTabChildItem
     5.77%  plasmashell  libQt5Quick.so.5.12.0  [.] 0x0000000000206bd6
     3.93%  plasmashell  libQt5Quick.so.5.12.0  [.] QQuickItem::childItems
     3.93%  plasmashell  libQt5Quick.so.5.12.0  [.] QQuickItemPrivate::prevTabChildItem