In that case I'd suggest using:
https://groups.google.com/group/zaproxy-develop
No specific reason, that option was added initially with that intention
but it was not actually implemented.
We don't have reports of that being a general problem, if the spider is
causing issues the active scan will probably cause more (it sends a lot
more requests than the spider, though the active scan does allow to
delay the requests).
Best regards.