I suggest you to do a test using 1 memory stick of DDR3L 1333/1600 1.35V, unplug the SSD and HDD. Try to update the BIOS to version 0249.
Download the .BIO file RY0249.BIO and paste it to the root of the USB2.0 thumb drive. Plug it to the NUC, power on the NUC and keep tapping F7, system will display the option to update the BIOS. It is possible to use the recovery option too.
BIOS Update Instructions for Boards and Kits