@grahamh Let me know whatever you need. Glad to help you…
Edit1:Btw. is it possible to whitelist/blacklist resolutions? So it would upscale to 3840x2160 from 3840x1600? Maybe LG C8 cannot display it.
Edit2: 3840x1608 works well 
Edit3: there has to be something with custom picture settings in LG. I played with settings and HDR that worked well stopped working. I did reset settings in LG TV and it played! Well well well, something weird is going on with LG…
Edit4: the one that played, then not, then reset display settings in LG and worked was the one with 3840x1608. 3840x1600 never worked with auto refresh rate.