This just an FYI to document this for any others that might experience the same issue.
Yesterday my laptop started spontaneously rebooting, then it started happening a lot.
I installed memtest86+ and found that if there is a DIMM installed in memory channel 0 then I get non-deterministic failures from 16 to 21GB in the memory map (I have 2x32GB DIMMS).
Installing a DIMM only in channel 1 results in a successful test.
I have been gaming lightly on this laptop (no more than an hour at a time, a few times over the last week) and suspect the thermal stress of gaming has exposed a faulty solder joint on the SoC BGA.
I have opened a ticket with FW support, I just wanted to document this for batch/lot tracking purposes.