Tried using Gen 2.0 PCI slot and didn't solve it either (for both cards).

Well, I did get these errors initially, but as soon as I started RMA process, the mofos @ AMD dropped a fix in the new AGESA and the issues stopped. I had no ground for RMA afterwards. I just needed a few more days before this new AGESA...

On your issue, I strongly advise you to try with another GPU, an AMD one preferably.

Weird that you didn't get the compiler error. I had a Malaysian post-week 25 chip and it didn't compile. This one is from China, so I just assume that it works.

I have considered it. I need to get another similar quality card to fully test.

My say is dump that GPU. Get a 580 and call it a day. 580 are dirt cheap now with all the crypto hype dead.

My 1700X is driving my 580 Nitro+ just fine. More so, my Ryzen is also from the 'bad' Malaysian batch, but I have 0 issues with it, even under Linux (I crunch & compile stuff).

Plus, as one of the chaps above said, some nvidias are having bad times running on Ryzens.

Good morning. I'm not sure if all of this is related to the problem I am encountering, I can confirm that I experience a similar phenomenon as you. 

I've already tried B. The stutter happens in games, but I don't know if the login issue is resolved in this setup. Here's what I have noticed, though. Try booting your machine, with monitors on, and do not login for something like 3-4 minutes.

Then when you go to login, I think you'll notice there is no hang or stutter. Which makes me think that it's NT Authority/System user logons that are causing the boot problem. Hope that helps.

Specs in sig. ASUS MG279Q 1440p 144hz freesync IPS monitor. I have 3 of them.

Back on win10 1709, when starting up the system, I would get 3 distinct "stutters" that each lasted about a second each when loading into the desktop (the mouse cursor would freeze, then play catchup 3 times). It also stuttered once when opening certain apps, such as a picture viewer for a jpg file, or opening a video with media player classic.

I found that less attached monitors caused less on bootup stutters. Windows 7 did not eliminate the stutters but they were a little shorter in length. Windows 10 1803 moved the stutters to between OS load screen and desktop login screen (usually hanging on a black screen or spinning pinwheel from OS load for a little time).

I tried a different NVIDIA video card (I think it was a 1060 6GB instead of the 1080 ti I have installed) and the stutters were the same.

The other paths I have yet to confirm is A: Try an AMD video card and B: Try different monitors. I can't do A as I sold my last AMD card but I may be able to squire another one soon. B is possible to try, but it's a pain to set up physically. Let me know if you have any feedback on my similar (?) situation.

Sadly, I had already tried this. But appreciate the reply.

The current GPU is EVGA Superclocked Nvidia GeForce 1060 GTX 6GB. I will explain...

Precisely.

I can. Let's go... (I've done this many times, but I think I need to clarify again for pure detail).

In January 2018, I purchased every single part and assembled this myself. 

The parts list included (swaps included in list):

I also use a USB soundcard, which I have tried to test with and without, sadly without any notable changes. Focusrite Scarlett 6i6. 

My mouse is a Microsoft Intellimouse 1.1.

Each time I have changed a component, I have attempted to be methodical about how I go about testing. I have disabled a lot of Microsoft services since my latest install. I am still sadly experiencing the stutter. Though, I feel I am in a better position to diagnose the issue as so much software has been removed from the equation.

OH! It might be worth mentioning that I have tried with and without GPU monitoring software installed. I have also removed BIOS overclocks to my CPU and run at stock. I have also tried to disable SMT (Simultaneous Multithreading). My temperatures are good (30-50 at load), and never seem to exceed 78C when stress testing with Prime95 under the heat stress.

I have tried various chipset updates, network, audio, and ATA/ATAPI drivers. I have obviously disabled a looot of stuff.

But, obviously, if it exists under Linux, it would point to hardware.

I hope this helps. Any further questions, please ask.