In my car, with the phone connected via Bluetooth, I can open Google Assistant by pressing the steering wheel button. I can then say, "Run <task name> with Tasker" and it will work, but only if the phone screen is on. If the screen is off, GA responds with, "Sorry, I didn't understand that".
I believe this to be an issue with Tasker (rather than GA) because, under the same conditions, I can run other apps with no problem. Tasker is the only one that fails this way. Thus, it's a failure unique to the GA/Tasker integration.
Some important information: