This bug is really hard to reproduce on Windows. It depends on flake8 is run. It's a random crash in the last GC collection at Python exit.

Crash related to AST in interpreter_clear() remains me bpo-41796.

Extract of the code:

static void
interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
{
    ...
    _PyAST_Fini(interp);
    ...
    /* Last garbage collection on this interpreter */
    _PyGC_CollectNoFail(tstate);
    _PyGC_Fini(interp);
    ...
}

The crash occurs in _PyGC_CollectNoFail().

_PyAST_Fini() clears references to AST types in the interpreter AST state. AST type instances hold a reference to the their heap type:

static int
ast_traverse(AST_object *self, visitproc visit, void *arg)
{
    Py_VISIT(Py_TYPE(self));
    Py_VISIT(self->dict);
    return 0;
}

But the crash happens when self->dict is deallocated.