Mysterie: result of executing command depends on initiating source

Dear reader,

I’m facing something that i can’t understand and i hope an expert here can shed some light on it.
In an automation i have the following command that sets the screen time-out on my OnePlus 15 on Android 16:

 - action: notify.mobile_app_name_of_phone
    data:
      message: command_screen_off_timeout
      data:
        command: 15000

The strange part is: when i activate this command from my PC or Chromebook it works like a charm. The screen time-out is immediately set to the correct value.
However, when i execute the exact same command on my phone it doesn’t do a thing. There is no error or warning or anything else, the command executes but it just doesn’t adjust the screen time-out.

“Allow systems setttings” on my phone is granted for Home Assistant. I also have some other commands (for example for screen brightness) that work fine, independent from the source that initiates the command.

Does any expert here has a clue how this is possible and how i can eventually solve the problem?

Thanks in advance,
Jack,