Update:
After working thru all this on my box I have actually made some minor progress.
As for resolving the screen pause\freeze issue completely I haven't, but from this work I have successfully affected the frequency (slowed them down) at which they occur & have somewhat narrowed the parameters in which to expect 1 to occur.
Since doing all this work it has demonstrated that the CPU processing efficiency will affect their occurrence.....the more efficient the CPU is at processing instructions (which also includes ISR's & DPC's) the less these will show up as there will be less chance of a buffer underrun happening if these are processed as fast as the CPU can process them & get the data in the L3\system mem cache to reduce the amount of time that the CPU isn't handling the other tasks that also need to be done. This doesn't explain the actual cause but can certainly reduce the issue & at the same time increase system productivity.....which is a good thing.
The next item is that after doing all this I have seen that the pattern of these screen pauses\freezes occurring has narrowed somewhat in that I have noted that when playing the game now, as long as the gameplay sets up scenarios that call for my box to increase performance due to increased work loads, I haven't witnessed a screen pause\freeze to occur & as long as the high work loads remain which maintain the high CPU\GPU work loads I haven't witnessed a screen freeze\pause occur. It is only now during the transition time from high CPU\GPU work loads to lower CPU\GPU work loads is when I have noted screen pauses\freezes to occur, not all the time do they appear during this slowing down period but the pattern does show the odds of 1 occurring during this particular time in gameplay is very high relative to any other time. My MSI AB graphs have consistently captured this happening but in times past the CPU side (CPU usage % clearly drops off on the SINGLE heavily loaded CPU core ONLY that the game threads are being processed on when the GPU clocks & FPS drop & GPU frametime spikes up then ramps back up when the GPU side does on recovery) didn't show itself as clear as it is now. I do know that AMD's Cool & Quiet isn't the cause as they still occur regardless of whether this is enabled or disabled in UEFI.
The game doesn't stop running, sound is never interrupted, control input is good, only the screen (video) is affected. Latency Mon is showing the only drivers to be showing any significant ISR's\DPC's are the Windows Driver Mode Framework Runtime(wdf01000.sys), Directx Graphics Kernel (dxgkrnl.sys) showing no ISR's but several DPC's & the Windows NT Kernel & System--the heart of Windows OS-- (ntoskrnl.exe) to a lesser degree showing no ISR's but a few DPC's. These are the top 3 drivers that consistently show the highest instances of ISR's\DPC's....everything else is FAR less.
I loaded the AMD Crimson 17.8.1 drivers specifically due to the release notes stating that AMD had fixed intermittent crashing in GTA V.....this game exhibits the exact same graphics screen pausing\freezing as AHIII Dx11 is showing in the exact same manner so I was hoping that this "GTA V fix" would resolve this in AHIII.....and as happened in times past.......appeared to had done so but they eventually came back. There is a tool developed to access vUEFI's for AMD Polaris & Vega cards called WattTool that can be used to make changes but I haven't ran into anything to allow access to AMD Fiji cards yet.
In closing I have a good sense of what is not causing these from a program standpoint. Looking thru the Services side of Windows I have reset a fair amount of these services to "Manual" once I checked them for any dependencies on other services or other services needing them to be active & all is operating very well w\o issues & Windows still checks out as clean so whatever the cause is IMHO it has to be something somewhere in the graphics interaction pipeline between the CPU thru to the GPU w\ anything else going on being an influencer\aggravator to the actual cause. In TM my box shows to have anywhere from 115 to 125 processes running in Windows 10 Home so I will need to be doing a LOT of Bing'ing my Windows 10 services to get more indepth detail on which ones that I can safely disable to lower this some but to date I have found no ill effects from all these processes running so far that I can tell.
Gonna move on to other things for now. Will revisit this after some more study time.