Mac OS X screens and updates

[Pic0o]

I have done some maintenance on Mac laptops before and have a Mac Mini myself.  I haven't had any issues with the Mini, but I did with a 2015 Macbook Pro.  Initial issue was some screen damage that looks like a residue stuck on the screen.  Turns out that was an issue with some Mac models, including the Macbook Pro 2015 model due to the anti-glare coating they used.  Fortunately, since they got their laptop at an Apple store, they had 4 year coverage and the repairs were free.  There is also a recall / free replacement for the logic board.  That repair was $575, before the cost was zeroed out because a warranty repair.  The new screen was crystal clear again and the laptop continues to soldier on.  We got this repaired in January of this year.
 

Item Number	Description	Price	Amount Due
S1586LL/A	Labor Charge, PBG4/MBP15"	$ 100.00	$ 0.00
S5741LL/A	Flat Rate 2 Repair Charge MBP15/MBP17	$ 475.00	$ 0.00
Total (Tax not included)		$ 575.00	$ 0.00

Lo and behold, I was visiting a couple days ago, and the same MacBook Pro (2015) rebooted to give the following error:
[auth] failed to write file <private>
At the bottom of an error log display.  if you have an nvidia MacBook Pro 2015) and update to 10.13.4, you're gonna have a bad time. https://discussions.apple.com/thread/8338509

I followed the suggestion to select the Boot Disk option, then to pick the Mac Hard Drive to have it boot normally.  This 10.13.4 issue looks to have just started again the other day (5/30).  Hopefully an update will address this, because a recovery log screen is pretty daunting, especially for someone who does not normally see error logs, as I will generalize and say is the case for many Mac users who do not work in tech.  Needless to say they were happy when I got it to boot back up and she will continue delaying the prompts to install updates on OS X.