I have just now also the same problem.
I have not deleted/unlinked homeassistant via the google action console. Only unlinked via the google home app.
When i want to link again via the app i get the login information of my home assistant, fill it in, waiting but it goes back to the list and will not link it.
What is exactly the solution now?
If this happens after some time, are there any log/debug where i can check that and correct that on time?