So, this worked for me on the 2019 shield. I'm using an old harmony one, the old logitech harmony software for mac, and just picked up a v2 flirc, and a 2019 shield pro. The activity created w/the flirc would turn off everything, but it would not turn on. I did notice that when i hit the "ok" button on my logitech, it would power on the 2019 shield. So, i added this into the startup sequence, but reviewing the activity and "adding more control". This allowed me to add the "ok" button into the sequence. working well right now.
Edit: Also works on 1st gen flirc.