I have an iOS app where most users can access the app normally, but a small number of users are unable to enter the app or load its content. For affected users, the iOS logs show errors such as: An SSL error has occurred, and a secure connection to the server cannot be established. or: A TLS error caused the secure connection to fail. The failure happens during the initial API requests, particularly the guest-login request. Because guest login fails, the app cannot proceed to fetch the home-screen data. Backend setup Backend is hosted on AWS API is served over HTTPS Domain uses an A record There is currently no AAAA record TLS certificate is valid Most users can successfully connect to the API The issue appears to be intermittent and affects only some users/devices Could this be caused by something other than my AWS server itself, such as: ISP/carrier routing issues TLS handshake problems IPv4 routing DNS resolution AWS networking TLS/certificate-chain configuration iOS URLSession behavior Network path differences between regions Some IP reputation/blocking issue Since I only have an A record and no AAAA record, could IPv6/NAT64 still be relevant to this problem? What would be the best way to diagnose this systematically? I am particularly interested in knowing how to determine whether the TLS connection is failing before the request reaches AWS, versus the request reaching AWS and failing somewhere in Nginx/backend. Any suggestions for tools, tests, or logs that would help isolate this would be appreciated.