I've created slave VM image with Packer and configured GCP cloud in Jenkins settings according to this guide.

When I start job requiring "windows" agent Jenkins starts to provision agents in a loop about every minute until I notice 10+ new agents and cancel the build.

I've attached one "iteration" of "provision loop", which seems to indicate that Jenkins doesn't honor 300 second launch timeout and prematurely gives up on agent and starts to provision next one.