It is unlikely that you hit the rate limit mechanism for your selected domain, as it is set to allow 10,000 certificates in LabCA.
If this LabCA instance is set up to (also) allow official domains (not recommended), then for the other domains the main limit is
Certificates per Registered Domain: 5 per 24 hours. As per the
Let's Encrypt™ rate limits page ,
a registered domain is, generally speaking, the part of the domain you purchased from your domain name registrar. For instance,
in the name www.example.com, the registered domain is example.com.
In new.blog.example.co.uk, the registered domain is example.co.uk.
The other limit is the Duplicate Certificate limit of 2 per 90 days. This applies to renewals when the old dertificate is still valid.
Revoking certificates does not reset rate limits, because the resources used to issue those certificates have already been consumed.