Why NO_MATCH system Google Assistant event is not triggered?

Question

I have the following setup of my Google Action -

Types - GAMEMODE:

• survival
• creative

Intents - CMD_SET_GAMEMODE:

• training phrases:
  • change game mode to creative
  • apply creative game mode

Scenes - COMMANDS:

• Custom intent handling
  • When CMD_ANOTHER_COMMAND is matched
  • When CMD_SET_GAMEMODE is matched - Transition to CMD_SET_GAMEMODE_SlotFilling

Scenes - CMD_SET_GAMEMODE_SlotFilling:

• Condition: if scene.slots.status == "FINAL" call my webhook
• Slot filling
  • gamemode: prompts for NO_MATCH - default values

Here is what happens when I test the dialog -

1. input change game mode to survival - works fine, my webhook is called
2. input change game mode - getting Sorry, My Action isn't responding right now. Please try again soon.
3. input change game mode to something - getting Sorry, My Action isn't responding right now. Please try again soon. When I check the log, I see that the error happens with endConversation event at CMD_SET_GAMEMODE_SlotFilling scene.

I don't understand why NO_MATCH prompts are not used?