To those who were affected by this event, you will be able to attempt issuance again in ~3 hours per https://letsencrypt.org/docs/rate-limits/
You can create a maximum of 10 Accounts per IP Address per 3 hours. You can create a maximum of 500 Accounts per IP Range within an IPv6 /48 per 3 hours. Hitting either account rate limit is very rare, and we recommend that large integrators prefer a design using one account for many customers.