IPv4 Uplink packet is filtered in tcap dump

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The device were configured to use Ipv6 APN. then a IPv4 related url (without domain ) was browsed to download a file. from the tcp dump pcap, it was noticed that all IPv4 Uplink packet is not seen. Only downlink packets are seen. The IPv4 is seems to be a private IP . The device was also downloading the file by using IPv6. No issue seen on IPv6