I just wanted to close an open from a much earlier thread back in July 2017 (Post 1573).
I also have a Chromebox with the Celeron 2955U which I also assumed included AVX2 since it's Haswell...
Intel® Celeron® Processor 2955U (2M Cache, 1.40 GHz) Product Specifications
If you look at "Instruction Set Extensions" you'll notice for the Celeron it only goes up through SSE4.2......
On the i3-4010U version of the Chromebox it does include AVX2 extensions.
I had been using the "archived" version release for awhile before deciding to update to an AVX build the other day. Thought it went fine until it went to go reboot after the update and hung at boot. Was perplexed but now understand it's due to the fact my core doesn't actually support those instructions 
I'm assuming no one else will run into this given how old those Chromeboxes are now, but just in case thought I'd share.
Does anyone know what the "intel-core-a" folder is for? If nothing else the cherry-trail build or base-generic version should work. Guess this goes back to the adage "if it ain't broke don't fix it"...
Thanks to escalade for the effort, upkeep, and help!