ESP8266 cause reboot randomly - nonOS SDK - please help

[johnxue]

I am working on ESP8266 board (ESP-wroom-02), and use wifi-ap, it works fine most of time, the device can connect to it and sends/receives data without problem. However it will reboot randomly if letting it run for awhile, sometimes it reboots within 30 minutes, sometimes it reboots after several hours. Multiple boards have been tested, all of them have same problem.

The following 2 line message are shown from serial port right before rebooting, then it will reboot immediately:
"tx rts error 0x16"
"mac 1370"

I am using arduino IDE with ESP8266 sdk v2.7.4, nonosdk, I have spent so much time to identify the issue, however I have no clue so far.

I suspect it has something to do with Nonos_sdk, and but there is no source code to let me tracking down where and how the issue occurs.

NOTES: I must use ESP8266 SDK v2.74 (or lower), but cannot use greater than v2.7.4, since I need to use lwip v1.4 compile from source option, and high version sdk doesn't have this option but only lwip v2.0, which is not suitable for our project.

Please help to resolve this issue.
Thanks in advance.