Ползунок контроля момента проигрывания аудиофайла работает не так, как я планировал.(PyQt 5, Python 3)

Такие ошибки очень тяжело искать !

1. в методе player_state вы self.Play_Pause написали с заглавной буквы, вместо self.play_pause
2. в этом же методе вместо self.play(self.song) - надо self.player.play()
3. в методе __init__ - self.play_repeat = True

Пробуйте

from PyQt5 import QtCore, QtWidgets, QtGui, QtMultimedia

class MyWindow(QtWidgets.QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.dict = {
            'bibi.mp3': [], 
            'D:/_Qt/EXE/Mp3/new_build/QThread_mp3/img/zvuki_prirody.mp3': []
        }
        self.song = ''

        self.player = QtMultimedia.QMediaPlayer()
        self.player.stateChanged.connect(self.player_state)

        self.qsl = QtWidgets.QSlider(QtCore.Qt.Horizontal, self)
        self.qsl.sliderMoved[int].connect(self.set_play_position)
        self.qsl.sliderReleased.connect(self.slider_released)
        self.qsl.setEnabled(False)

        self.box = QtWidgets.QGridLayout(self)

        for line, song in enumerate(self.dict):           
            play_btn = QtWidgets.QPushButton('Play', clicked = lambda ch, song = song: self.play(song))
            pause_btn = QtWidgets.QPushButton('Pause', clicked = self.pause, enabled = False)

            label = QtWidgets.QLabel(song)
            self.box.addWidget(play_btn, line, 0)
            self.box.addWidget(pause_btn, line, 1)
            self.box.addWidget(label, line, 2)

            self.dict[song].append(play_btn)
            self.dict[song].append(pause_btn)

        self.play_repeat = True                                                   # - False / + True

        self.repeat_btn = QtWidgets.QPushButton('Repeat', clicked=self.repeat)
        self.box.addWidget(self.qsl, 2, 0, 1, 3)
        self.box.addWidget(self.repeat_btn, 3, 0, 1, 3)

        self.play_pause = True
        self.timer = QtCore.QTimer(self)
        self.timer.timeout.connect(self.play_mode)
        self.timer.start(1000)

    def play_mode(self):
        if self.play_pause == False:
            self.qsl.setMinimum(0)
            self.qsl.setMaximum(self.player.duration())
            self.qsl.setValue(self.qsl.value() + 1000)

    def slider_released(self):
        self.player.setPosition(self.qsl.value())

    def set_play_position(self, val):
        pass

    def play(self, song):
        if self.player.isAudioAvailable() == False:
            self.player.setMedia(QtMultimedia.QMediaContent(QtCore.QUrl(song)))
            self.dict[song][1].setEnabled(True)
            self.song = song

        if self.song == song:
            pass
        else:
            self.player.setMedia(QtMultimedia.QMediaContent(QtCore.QUrl(song)))
            self.dict[self.song][1].setEnabled(False)
            self.dict[song][1].setEnabled(True)
            self.song = song

        self.player.play()
        self.play_pause = False
        self.qsl.setEnabled(True)

    def pause(self):
        self.player.pause()
        self.play_pause = True

    def player_state(self, state):
        if state == 0:
            self.play_pause = True                         # -Play_Pause / + play_pause
            self.qsl.setSliderPosition(0)
            self.qsl.setEnabled(False)
            if self.play_repeat == True:            
                self.play_pause = False                    # -Play_Pause / + play_pause

###                self.play(self.song)                    # ---
                self.player.play()                         # +++



    def repeat(self):
        if self.play_repeat == False:
            self.play_repeat = True
            self.repeat_btn.setText("Repeat")              # +++    
        else:
            self.play_repeat = False
            self.repeat_btn.setText("Not Repeat")          # +++ 


if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    window = MyWindow()
    window.setWindowTitle('MP3-player, PyQt5')
    window.show()
    sys.exit(app.exec_())