I think there's a problem in the tree structure of IfcProfileDef types in the demo library :
https://github.com/IfcOpenShell/IfcOpenShell/blob/v0.6.0/src/blenderbim/libraries/blenderbim-demo-library.ifc

IfcCircleProfileDef and IfcRectangleProfileDef are apparently referencing themselves, leading to possibly infinite recursion when traversing the tree. Also their children IfcCircleHollowProfileDef and IfcRectangleHollowProfileDef are also present at the same level as themselves.
I nosed around the Ifc file but I'm not fluent enough in ifc to solve the problem by tweaking values :)