A company runs a software solution on EC2 instances in a cluster placement group. The application's UI is a single HTML page (1,024 bytes). The software also processes files larger than 1,024 MB and serves those files to clients on request. Files are shared with the Don't Fragment flag, and the EC2 instances' ENIs are configured for jumbo frames. The UI is always reachable from allowed source IPs regardless of whether clients are in a VPC, on the internet, or on premises. However, clients sometimes fail to receive requested files because the files do not travel successfully from the server to the clients. Which of the following could be root causes of these failures? (Choose two.)

The problem describes large files failing to transfer, while a small UI page always works, and the Don't Fragment (DF) flag is set. This indicates a Path MTU Discovery (PMTUD) issue. When the DF flag is set, if a packet exceeds the MTU of a link in the path, it will be dropped, and an ICMP "Fragmentation Needed" message should be sent back to the source. If this ICMP message is blocked, the source never learns to reduce its packet size, leading to dropped packets and failed transfers for large files. Both AWS Site-to-Site VPN and public internet connections often have MTU limitations lower than the 9001 bytes used by jumbo frames in EC2. If ICMP is blocked along these paths, PMTUD fails. Direct Connect typically supports larger MTUs and is less likely to cause this specific issue. The security group not allowing ICMP traffic or the OS not supporting jumbo frames are incorrect because the problem states ENIs are configured for jumbo frames and the UI is always reachable, implying basic connectivity.