Looking at your account, I can see your Allocated IPv4 Elastic IP addresses:
$ aws ec2 describe-addresses | jq -r '.Addresses[].PublicIp'
13.36.xxx.yyy
13.36.xxx.yyy
13.37.xxx.yyy
Connecting to two of your containers, and looking at the outgoing IP address, I clearly those listed above:
$ dig +short txt ch whoami.cloudflare @1.0.0.1
"13.37.xxx.yyy"
$ dig +short txt ch whoami.cloudflare @1.0.0.1
"13.36.xxx.yyy"
This works on your production cluster because you’ve configured “Static IP” as @rophilogene mentionned. However it’s not set on your dev cluster, so it’s not possible to whitelist IPs.