Finally tracked down and came up with a work around for that weird bug. Sometimes i3's input gets into a weird state, I think because some windows either don't close properly or move the focus somewhere it shouldn't be. Either way it breaks keyboard input completely even though i3 itself is fine. Added a watchdog to check for this condition and reset i3 if it happens. Sure, your desktop may pop up but it beats the hell out of a frozen GUI.

scripts/sound.py

@@ -50,13 +50,20 @@ def on_new_window(self,i3):
 
 def on_close_window(self,i3):
     try:
-        windowName = getattr(i3.container, 'name', None)
-        windowClass = getattr(i3.container, 'window_class', None)
+        # Get container early - if this fails, bail immediately
+        container = getattr(i3, 'container', None)
+        if container is None:
+            return
+
+        # Fast checks with immediate bailout on any issue
+        windowName = getattr(container, 'name', None)
+        windowClass = getattr(container, 'window_class', None)
+
         # Skip sound only for notification daemon (it has its own sound)
         if windowName != 'xfce4-notifyd' and windowClass != 'xfce4-notifyd':
             play_sound_async('play -nqV0 synth .25 sin 880:440 sin 920:480 remix - norm -3 pitch -500')
     except Exception:
-        # Silently ignore errors to prevent blocking i3
+        # Silently ignore any errors - better no sound than blocking i3
         pass
 
 def on_mode(self,event):