I think you need to ensure that battery optimization is off for this app and that it's allowed to run in the background.
If you don't know how to do it, someone might be able to assist if you tell us what phone you have.
For the home button version:
It must be set as the Assist app. On my phone it's under Settings/Apps/Advanced/Default app settings/Assistance & voice input. Then set the Assist app as Google Assistant.