As reported in https://bugs.openwrt.org/index.php?do=details&task_id=3094 I have found that in the TP-Link Archer C7 v5 hardware (QCA9563) running OpenWRT I can't see most packets in a tcpdump capture while in a TP-Link Archer C7 v2 hardware (QCA9558) all the packets are there. While the kernel version is relatively old this can be reproduced even with the latest commit of OpenWRT, which uses the backports project to run the latest drivers. Happy to provide remote access to the devices or to send samples of them by post if it helps.