Socket connection failure for t-mobile only on iOS 10.2

We are doing SSL certificate verification using Chilkat. T-Mobile enforces IPV6 in iOS 10.2. SSL socket connection using Chilkat always fails for us on this particular operator / OS combination. However, when we open an HTTP connection from the same device to the server (also on IPV6), it seems to connect fine. Our server is not IPV6 ready, but i'm kind of curious why the http connection works fine on IPV6 and the socket does not.

Unable to connect: ChilkatLog:
  Connect_Socket:
    DllDate: Mar  6 2015
    ChilkatVersion: 9.5.0.48
    UnlockPrefix: AUGMENSocket
    Architecture: Little Endian; 64-bit
    Language: IOS Objective-C
    VerboseLogging: 0
    objectId: 3
    Connect_Socket:
      hostname: api.hostname.com
      port: 443
      ssl: 1
      maxWaitMs: 10000
      socket2Connect:
        connect2:
          connectImplicitSsl:
            connectSocket:
              connect_ipv6_or_ipv4:
                socketErrno: 51
                socketError: Network is unreachable
              --connect_ipv6_or_ipv4
            --connectSocket
          --connectImplicitSsl
          ConnectFailReason: Connection rejected
        --connect2
      --socket2Connect
      Failed.
    --Connect_Socket
  --Connect_Socket
--ChilkatLog

Does anyone have insights on why this may be happening?