What is the problem with `PySet_Contains` when calling Py func in C?

Question

I write C source code like this, aiming to accelerate the Python code with C, so I include some py object and func in C:

• include header file Python.h and dynamic link file libpython3.8.so.

// test.h
#include "Python.h"
#include <stdio.h>

// test.c
void main(){
    PyObject *bigrams1 = PySet_New(0);
    
    ret = PySet_Add(bigrams, PyUnicode_FromWideChar(L"nc", 2));
    ret = PySet_Add(bigrams, PyUnicode_FromWideChar(L"ckd", 3));
    ret = PySet_Add(bigrams, PyUnicode_FromWideChar(L"nc.3e", 5));
    // and I check the following if the nc string in in bigrams:
    ret = PySet_Contains(bigram, PyUnicode_FromWideChar(L"nc", 2));

}

• In this code I create a Python set object and add three string to it, 'nc', 'ckd', 'nc.3e'. The strings added to the set are random, this is not the key point of the problem.
• and when I check if 'nc' in bigram, which correspond to the PySet_Contains func, the running code corrupts.

./test: line 10: 2976044 Segmentation fault      

But when I change the nc to other strings like anyone else 'ok', 'ckd', 'project', the code was running correctly. Only the nc caused the bug.

What is the problem with the code and the strange string nc?

Additional description

• I tried both Python3.8 and Python3.11 and the results are the same.
• I tried thousands of other strings like '中国', 'few', '$$####', '1e32e2', all the other strings work well.
• That's the strange string 'nc'.