I just had a simple question, why does the VCCIO voltage on the Z370 Gaming K6 board become red @1.15 volts, and normal below that?  I've heard that as long as VCCIO is below 1.2 V everything should be fine.  If I set the voltage to auto AIDA64 reports it as 1.216 V, and in BIOS auto is set to 1.2 V (which makes sense).

Secondly, what are the max safe voltages for VCCIO and VCCSA on this board?  I've also read that VCCSA should be kept below ~1.25 V.

Also third, do the VCCIO and VCCSA voltages affect the core temperature during stability testing (or any load)?

Lastly how does VCCIO and VCCSA voltages affect memory tests, if at all?  A month ago I tested my new memory stick (4x16 GB G.Skill Trident Z RGB, 14-14-14-34 timing) at stock CPU speeds and everything was fine.  Today I tested it and actually had 3 errors over 2 passes of 4 total passes.

VCCSA can help with CPU overclocking, especially with 'borderline' stable overclocks - from my experience with multiple different motherboards (from numerous manufacturers), increasing VCCSA has an impact on VCORE.

I only recently moved to Coffee Lake from Skylake, although the architecture is an extension of Skylake (that includes Kaby Lake), but with Skylake VCCIO was usually in the 1.12 - 1.20 range and for higher overclocks VCCSA up to 1.25V
Some people have gone to 1.35V on VCCSA with Z370 boards, but it's generally felt that keeping both VCCSA and VCCIO below 1.25V is best practice - VCCIO in my usage is always lower than VCCSA. 
Usually 1.15-1.17 on VCCIO and 1.17-1.20 on VCCSA.
 

If you want to know the real voltage you should use a multimeter on the back side of the MB socket - there's plenty of videos on how to do this. Motherboard sensors an often be quite innacurate. 

If you are having memory issues, what are you using to test?
Memtest is still what I would consider the gold standard but needs to be run from a USB thumb drive in it's own boot environment.

Are you using XMP profile? Some memory is hit or miss and needs manual settings rather than the XMP settings. Seems I've known more people with issues using the Trident Z brand than most others.

Sorry for the late post. 
I've been going down my own OC journey with this board - well, the z370 Extreme4 - but in the same ballpark as the Taichi - I just had no need for WiFi.

I never had issues with RAM stability, I just ran the XMP profile and it worked. But my RAM is only 3200Mhz.

As for the VCCIO and VCCSA, the 'auto' amounts are way too high IMO.
I found another user who used values that worked for me with my older z170x Skylake board, and since I am still using the same RAM I figured I would go backwards.
As you know less VCCSA in particular lowers vCore, so I am at 1.17 VCCSA and 1.14 VCCIO and just completed an 8 hour overnight stress test (8086K at 5.1Ghz across all cores and GTX1080ti at 2063Mhz) in Realbench, preceeded by a 4 hour Prime95 test.

I would say that your settings are definitely on the high end and I don't think they are what's causing your stability issues. Some RAM just doesn't play nice with certain boards and often down-clocking a little resolves the issues.
In all seriousness 4200Mhz DRAM isn't going to give you any noticeable performance boosts in every day usage (whether that's productivity or gaming), and you will only see a difference maybe in synthetics.
DRAM speeds have become a marketing gimmick - at the end of the day the CPU will always be the bottleneck as there's nothing that can keep up with DRAM speeds.

Linus Tech did a nice article on DRAM a while back which saved me a lot of money (and stability issues) going for lower speed (still overkill) DRAM:

As for longevity, I would not worry about it even at those values. I doubt you will have any issues even if you kept the PC for 10 years, but at the 5 year point it will be close to irrelevant to be honest, so beyond that you will be running into issues that are much more pressing than voltages.

Good luck!

The worst part is that it takes time I could be spending trying to help users to deal with problems.