[snyft]

LG TV and a ASUS Monitor, Nvidia 1060x6 with basically the same hook-up, waspi, hdmi, Onkyo TX-SR333 to the TV and DVI to the asus monitor. 1080p x 60hz all round, all is jake. Of course I use the TV as my second monitor, either in twin, extended or single on either side using the display switch.

This is a little different "Display marantz-AVR (MJI0035 EDID Override)" pulling out the AVR might make sense here, and this "resizing due to size change (1920,0,3840,1080 fullscreen)->(1920,0,3840,1080 fullscreen)" looks like some confusion as to 1080p vs 4K in the same line...Is your TV 4K? From your post "1060GTX, 1080p 60hz on both monitors"  you might want to white list only the obvious resolutions on your test set-up. If you run in windowed mode on the desktop, are you having the same issues?

I see. Is your LG tv HDR? 
My tv is 4k but my cables can't handle 4k so i run it in 1080p. I have white listed only 1080p resolutions and 720p. 
I tried fullscreen window before that did not work, but as you said windowed mode works!

Edit: Got my new cables that support 4k60 and running Kodi in 4k does not fix the problem sadly