A year ago I bought an Acer Chromebook 315. Using Mr. Chromebook to get Chrome to boot from USB, I did a dual installation of Linux Mint Mate. Now I want to do a clean install with Cinnamon, however, my computer gives me an error saying a 64-bit OS is not on the disk. I tried making the installation disk with a different program (etcher) and a different USB stick but I still get the same results. My computer will boot the original Mate USB installation stick. As a work around, I installed the cinnamon desktop via command line. It has the same results.
Have you taken a look at the docs for the project here? Have you installed mrchromebox firmware via RW_Legacy or Full UEFI ROM?