I suggest you try 0.7.0-rc.6, as there have been a number of bugfixes/enhancements introduced to SoftAP/HTTP server implementation in 0.7.x versions: https://github.com/particle-iot/firmware/pull/1362
Your wireshark logs look quiet similar to what I was seeing when the web browser was bombarding Photon with several concurrent HTTP requests and it couldn’t handle that properly.