Hey. I had the same issue as above with the same crash log. I tracked the issue down to tank.platform.engine line 1563: if not QtGui.QApplication.instance():. It seems to be getting an instance of the QApplication that causes the crash.
After a bunch of messing around it seems that if you’ve accessed the QApplication before the engine starts, it doesn’t crash.
This is horrendous hack but I’ve added the following to plugin_bootstrap.py at line 85 just before the engine starts:
from PySide2 import QtWidgets
QtWidgets.QApplication.instance()
I don’t know exactly what is going on but, for me, this no longer crashes. It’ll do until ShotGrid release official support.
ETA: This is even weirder. To make things a little neater I tried moving the above code to the start of plugin_bootstrap.py. That crashes instantly. Something is going on around there that makes Houdini particularly fragile when accessing the QApplication.