Predefined CloudFormation stack running as root causes "CodeBuild is not authorized to perform: sts:AssumeRole on service role"

I’m working on deploying an AWS Telco Network and have followed the documentation in doing so along with their sample code, however on the final instantiation step I keep getting an sts:AssumeRole not authorized error. I tracked down the CloudTrail event and here’s what it looks like. Any idea to go about resolving this?