In case of creating clusters it is usually a 'big thing". Imean that creting such resource takes time.
I encountered situations, where cluster took longer to create in cloud, but pulumi already went further.
So in your case, I assume that pulumi assumed cluster is launched, while in fact in AWs it was still setup
So you can first confir this is the case, and check AWS status directly from console, or aws command maybe.
Aditionally I advise to use "depends" when creating resources
https://www.pulumi.com/docs/concepts/options/dependson/