I managed to fix my issue by doing the following on my android tablet:
- Remove the google home app
- Clear cache and data for Google Play Services
- Switched off the Google Nest Hub device & waited 5 mins
- In HA/settings/Thread then deleted the NEST thread network
- In the compansion app then did a sync credentials
all working now and my devices now get added to my “ha-thread-4dc3” network.
It shouldnt be this difficult though 