To avoid this issue, space your certificate orders out over time, combine commonly-hosted domain names into single certificates, or utilize multiple servers with different ACME accounts.
Sometimes this error can be a symptom of a malfunctioning ACME client that's failing and repeating orders.
For users of the ACME v2 API you can create a maximum of 300 New Orders per account per 3 hours. A new order is created each time you request a certificate from the Boulder CA, meaning that one new order is produced in each certificate request. Exceeding the New Orders limit is reported with the error message too many new orders recently.