Problem with function push_back() and push_front() with class list in c++

I'm trying to do this simple program, where I want to use the take and append functions, which access a buffer implemented with a list, in a producer-consumer problem:

#ifndef buf_h
#define buf_h

#include <list>
using std::list;
#include <mutex>
using std::mutex;
#include <condition_variable>
using std::condition_variable;

class Buffer
{
    public:
        Buffer(int cap);
        void append(int shift);
        int take();
        
    private:
        list<double> Buffer_;
        int capacity_;

        int count_;
          
        mutex mutex_;
        condition_variable not_full_;
        condition_variable not_empty_;
};

#endif

This is buffer:

#include "buf.h"

#include <list>
using std::list;
#include <mutex>
using std::mutex;
using std::unique_lock;
#include <condition_variable>
using std::condition_variable;

Buffer::Buffer(int capacity)
    : Buffer_(capacity,0), capacity_{capacity}, count_{0}
{
}

void Buffer::append(int shift) 
{ 
    unique_lock<mutex> mlock(mutex_);
    while(count_== capacity_)
        not_full_.wait(mlock);
    Buffer_.push_back(shift);
    ++count_;
    not_empty_.notify_one();
}

int Buffer::take() 
{
    unique_lock<mutex> mlock(mutex_);
    while(count_ == 0)
        not_empty_.wait(mlock);

    int w = Buffer_.front();
    Buffer_.pop_front();
    --count_;
    not_full_.notify_one();
    return w;
}

This is main:

#include <iostream>
using std::cout;
using std::endl;
#include <fstream>
using std::ifstream;
#include <thread>
using std::thread;

#include "buf.h"


Buffer B1{20};

void producer(int id){
    B1.append(id);
}

void consumer(){
    int w = B1.take();
    cout<< w <<endl;
}

int main()
{
    for(int i=0; i<5; ++i){
        thread prod(producer, i);
        thread cons(consumer);
    prod.join();
        cons.join();
    }

    return 0;
}

I don't understand why if I use push_back() in append, I get all 0 as output, when instead I should get this:

0
1
2
3
4

If I use push_front() the output is correct. Can anyone help me?