DNS-01 challenge fails since unbound 1.18. TXT records can be fetch using unbound 1.16 but not 1.18 1.19

Since [most] validations are cached for up to 30 days... [per account].
You could simply run the same request a few times in a row.
Each time anything is authenticated, it will be removed from the next request.
Eventually all will have been authenticated and the cert will be issued.

That said, there are rate limits that must be adhered to.
So, just play within the set limits and you can game a win.