Are running this on two different computers (or VMs)? It seems there are more variables involved than just 'different version of QtCreator'.
Working:
Qt 5.12.2 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 8.3.0) on "xcb"
OS: Ubuntu 19.04 [linux version 5.0.0-38-generic]
Environment:
QT_ACCESSIBILITY="1"
QT_AUTO_SCREEN_SCALE_FACTOR="0"
Not Working (note, QT_ACCESSIBILITY is not set):
Qt 5.12.4 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 9.2.1 20191008) on "xcb"
OS: Ubuntu 19.10 [linux version 5.3.0-40-generic]
Environment:
QT_AUTO_SCREEN_SCALE_FACTOR="0"
Do you have additional KDE packages (not sure what that the 'kdedev' folder is) installed on the one that's working? Does your application depend on them? Can you run it in debugging to see where exactly it is crashing?