I have a problem with cfn-init in my cloudformation template. By default, the cfn-init sends a successful signal to my auto-scaling feature, however it is not sending any signal to auto-scaling, and ultimately exceeds the timeout and starts the rollback in the stack.
I went to see the cfn-init.log logs inside the machines, and shows an exceeded timeout error when describing my launch configuration.
I checked my template code and it's normal, so much so that I've used the same code in another template and it worked. I'm in doubt that you might have some relationship with Network ACLs.