Generation of certificates for newly added domain is currently delayed due to a rate limit issue. A fix has been issued on our end and the situation should come back to normal in a few hours.
EDIT 19:16 UTC+1: This does not impact renewal of certificates.
EDIT 19:36 UTC+1: We are now under the rate limit, newly added domains should have their certificates generated in a few minutes, as usual. Sorry for the inconvenience.