A network engineer deploys an application in a private subnet in a VPC that connects to many external video feed providers using RTMP over the internet. A NAT gateway has been deployed in a public subnet and is working as expected. From the Amazon EC2 instance, the application is able to connect to all feed providers except one, which hangs when connecting. Manually testing a connection from an Amazon EC2 instance in the public subnet to the problem feed indicates that the feed works as expected.
What is causing this issue?

A. The NAT gateway does not support fragmented packets.
B. The internet gateway only supports an MTU of 1500 bytes.
C. An Amazon EC2 instance expects to communicate with an MTU of 9001.
D. The security group on the instances does not allow PMTUD.