It has been three days with my warranty replacement SB. So far, so good.
This SB has a build date of 2016 week 27. The old SB had a build date of 2015 week 40 (close to the very first batch made).
I had one hardware error shortly after setting everything up (LiveKernelEvent Code ab), but it didn't cause any actual problems and has not been repeated. I also had a couple of lag issues with Word 2016, but they may have been caused by an Adobe add-in which I have since removed.
Windows Hello has worked consistently (which was always only about 75% with my old SB).
The new SB wakes properly from sleep (so far), which was the most frustrating and prevalent issue with my old SB.
Fingers crossed. The old SB worked well for a couple of weeks after reinstalling Windows, so it is still too early to tell for sure.
glad it worked out for ya... most times all someone needs to do is a full wipe and restore, and if that doesn't help then get a replacement! too many times I've seen people abandon a surface product to immaturely and not give it a chance...