The same pi had two corruption in 6 weeks time, using the FTDI. So FTDI is not a fix for me. And internal serial port is not a solution.
I am pretty sure that one pi worked with the internal port, but, maybe it was a pi1 or pi2, and maybe the one that crashed again yesterday was a pi3. So, maybe the serial port on pi3 has less capabilities than on pi1 or pi2 ... or the custom ROM provided by KeiDei messes the serial port.
But I can not compare more criteria:
- one pi that never had any trouble has heat sinks, and average temperature over the month at 41°C, burnt with rpi_35_B_B+_PI2.img
- the pi that crashed 3 times in 6 months does not have heat sink, has an average temp of 49°C, and is using ROM rpi_35_v6_0_2_jessie_kernel_4_4_11.img
I remember that those two pi can not use the same ROM because they are using different versions of KEIDEI screens; if I use the image rpi-35-B on the pi that just crashed, I know the LCD won't work.