Thank you for the detailed explanation. I understand that a network or NAT-related issue could cause a persistent connection to become stale while the device still appears to have a perfectly healthy Wi-Fi connection. However, I have already tried several different configurations, routers, and Wi-Fi networks, and the issue seems to occur consistently across all of them. One aspect that makes the issue particularly difficult to understand is that it appears to affect VoWiFi specifically. Other third-party applications that maintain persistent network connections continue to work normally and do not appear to disconnect or require reconnection after the iPhone has been idle for several minutes. For this reason, I would like to better understand how I could test whether the network is actually contributing to the issue. Are there any specific tests, diagnostics, packet captures, or network conditions you would recommend checking to determine whether NAT timeouts, UDP/IPsec sessions, or another network-related issue could be causing the VoWiFi connection to become unavailable? I would be happy to perform any tests that could help isolate whether this is caused by the network, the carrier infrastructure, or iOS itself.