I’m not saying this is a good solution for the TVs that won’t turn on, but there is a workaround.
You can add a SwitchBot mini hub IR blaster for under $50. It has a smartthings integration in the new app. Then you can use Switchbot to turn the TV on and from there do everything else with the official tv features. That gives you complete voice control.
Again, I’m not saying this is a good solution or that they shouldn’t fix it, but it does work. I myself am quadriparetic so I can’t use the button remote. So I did this with my smart fire TV, which could do everything except turn on by voice.
Here’s my thread on that project. (The topic title is a clickable link)