ASG Won't Put Healthy EC2 Instances InService. Stuck in Pending.

I am having trouble getting ASG's to put healthy EC2 instances in service after it starts them. There are no lifecycle hooks. The instances are healthy, passed the EC2 status checks. I can shell into them. But the ASG never moves them from Pending to InService, and eventually it shuts them down.

I tried with a different AMI, subnet, VPC, spot instances, normal ones, and I get the same result. But this only appears to be happening in N. California. Things in N. Virginia seem to be working normally.

Can anyone help resolve this? Thank you!