AutoCast Autocast doesn't work all times when phone is locked

I have profile that shows a notification and casts an audio file to my Google Home mini when a calendar event happens. The profile works well (both actions) when my phone is unlocked. But it doesn't work all the time when the phone is locked. I see the notification but the audio file doesn't play on the Google Home mini unless I unlock the phone.
P.S my phone is Google Pixel 4

 

Thanks for your response. Currently, it works sometimes when it is locked but it is not very stable. Do you know if there is something I can do to improve that? Like, will rooting the phone help? or will remove the lock and keep the phone always unlocked help?