Something is terribly wrong with encryption on FXP318 imho. So, according to link above and other sources, "It needs to make sure the filesystem doesn't extend into the last 16 Kbytes of the partition where the crypto footer is kept." I boot to recovery and formatted /data:
# mke2fs -T ext4 -L userdata /dev/block/mmcblk0p27 2133871
I made 512kb, 32kb give the exact error.
Next, encryption didn`t start either and phone just rebooted, logcat showed "unmounting /data failed" before reboot. Google lead here
# while true; do lsof | grep /data; sleep 0.2; done
showed that sensord is not allowing unmounting. So I did
before final click to "Encrypt storage".
Finally, encrypting began and completed successfully (I thought so).
After reboot, phone is asking for passphrase and when I type it, green "decrypting" robot appears for a second and then black screen and phone is totally hanged and unresponsive, only removing battery helps.
I`m out of ideas