I've had a few freezes too with my M2 Ultra. Been using Ubuntu mate and adding additional apps. Thought it was just me trying to do too many things at once, but with lock ups and samba problems, this is not looking good. I hope this is software related and not hardware related. I have the pi3 but it's missing Gig NIC and SATA connection for my needs.
If I had bought this device from a local shop, I would have returned it by now.