Single Device Not Un-Muting (via Automation)

I’ve got a number of Google devices (primarily Nest Minis, though with 2 Nest Hub Maxs, and the troublemaker, a Lenovo Smart Clock Essential). I wanted to silence that irritating “cast noise” that Google devices make when you cast to them, and found some suggestions on Reddit. They largely work by muting the speakers (I have them in a group in the Google Home app) playing a silent sound, waiting a second, increasing the volume back to a proper level, and then playing whatever I’m casting.

The problem that I’m having is that the Lenovo device doesn’t automatically unmute. I’ve even tried adding an action into those automations TO unmute that speaker group, and it still doesn’t do it.

This is the relevent part of my automation. Any suggestions?

action:
  - service: media_player.volume_mute
    data:
      is_volume_muted: true
    target:
      entity_id: media_player.speakers
  - service: media_player.play_media
    target:
      entity_id: media_player.speakers
    data:
      media_content_id: media-source://media_source/local/1sec.mp3
      media_content_type: audio/mpeg
    metadata:
      title: 1sec.mp3
      thumbnail: null
      media_class: music
      children_media_class: null
      navigateIds:
        - {}
        - media_content_type: app
          media_content_id: media-source://media_source
  - delay:
      hours: 0
      minutes: 0
      seconds: 1
      milliseconds: 0
  - service: media_player.volume_mute
    data:
      is_volume_muted: false
    target:
      entity_id: media_player.speakers
  - service: media_player.volume_set
    data:
      volume_level: 0.5
    target:
      entity_id: media_player.speakers

Further oddness - if I cast to just that Lenovo device, even if it’s been previously muted by another automation (and I haven’t caught that it’s still muted) … it WILL play what’s casted to it at normal volume.

Am I missing something?