I switched on the iOS feature “Require Face ID” for the companion app. This worked as expected - when I open up the app, it does a biometric check to see if is me. Great!
However, there is a downside. It stops iOS shortcuts working, and iWatch configurations from running.
This is perhaps understandable, and I suspect there is no workaround.
I documented here to help others who switch the feature on, and like me, a few weeks later see things break. Might cutdown your debug time.