In sbkmodule.cpp, line 472, the original _import_ function is fetched from the builtins dict without incrementing the reference count.

If later the _import_ function in the builtins is replaced then the one held here will be destroyed leaving an invalid function object, which will cause a crash on the next import.

A Py_INCREF should follow PyDict_GetItemString, since that returns a borrowed reference:

 
static PyObject *origImportFunc{};
..
static PyObject *lazy_import()
...
origImportFunc = PyDict_GetItemString(builtins, "__import__");
Py_INCREF(origImportFunc)  // This is missing around line 473
 

 
It looks like this bug was introduced in commit 7accf7c3042e3f0680fa0615a0f13b54d28a0efd "LazyInit: Implement Lazy Initialization by Delayed Module Entries" https://codereview.qt-project.org/c/pyside/pyside-setup/+/539467