Got it working, but it's not better than before...

wobuzz/player/player.py

@@ -1,5 +1,6 @@
 #!/usr/bin/python3
 
+import time
 import threading
 import pygame.mixer
 import pygame.event
@@ -174,6 +175,15 @@ class Player:
     def start_playlist(self, playlist):
         self.stop()
 
+        if not playlist.loaded:
+            playlist.load()
+
+        while not playlist.has_tracks() and not playlist.loaded:  # wait until first track is loaded
+            time.sleep(0.1)
+
+        if not playlist.has_tracks():
+            return
+
         self.current_sound, self.current_sound_duration = playlist.set_track(0)  # first track
         self.current_playlist = playlist