'AWS IAM instance policy applying credentials to instance in one region, but not another

I have a setup where I launch AWS EC2 instances from templates and their AMI contains the AWS CLI, so it can copy over the contents of a private S3 bucket on launch. This template automatically applies an IAM role with the "AmazonS3ReadOnlyAccess" policy. This has been working as intended so far in the eu-west-2 region, but now I wanted to run these instances in us-east-2 region. I copied the AMI and made a new template using identical settings to the ones in eu-west-2, but when the script to sync the S3 buckets launches (it's just a bat file that runs "aws s3 sync ... ...") the contents of the synced folder are empty.

After a bit of looking around I noticed that it throws a "fatal error: Unable to locate credentials" error. I checked the credentials using "aws configure list" and get that access_key, secret_key and region are not set. If I run the same instance back in eu-west-2 these fields are populated.

I've tried recopying the base AMI, recreating the launch templates, creating region specific buckets, creating new IAM policies and all this as both a IAM user and the root user, the credentials still get set in eu-west-2, but not us-east-2. The only configurations that differ are the VPC, subnet and routing table settings - for obvious reasons, as they need to be in a new region. Does anybody know why this might be happening? As I've run out of ideas.

us-east-2a instance