Enable debug logging, clean boot, demo the problem with local medai, then "cat /storage/.kodi/temp/kodi.log | paste" and share the URL.
I went ahead and reinstalled LibreElec completely from scratch and for some reason it's not doing it now.. -shrugs-
Ignore how to install above. I figured it out. I am dumb 
I SSH'd into my server. installed the latest 12.0 nightly (which I think was uploaded on the 23rd?) ran the update using the following commands
systemctl stop kodi
wget -P /storage/.update https://test.libreelec.tv/12.0/Generic/G…-bbccdbb.img.gz
reboot
took a bit for the device to come back up. when it did most of my addons broke ( I guess they are not omega compatible yet?) but, I tried to play the local 4K files again to see if those were still giving issues and they were still doing the slow mode with audio running fine. tried a stream of one of the addons that worked in 4K and also still having slow mo 
Ok, Dumb question.. How do I download the nightly for LE12. When I go to the nightly download page > 12.0 > and latest release It says it's 238mbs but the file it downloads is SHA and only 128kbs big. am I doing something wrong? Sorry!
Also, any reason for me to do Nightly.v12.Generic_x86 or Nightly.v12.Generic_x86_Legacy?
Please test a current LE12 nightly .. let's see if newer kernel/drivers have fixed anything since LE11?
Will try and will report back.
Also, I tried a bunch of videos locally using 4kmedia.org and all of them did the same thing as the streamed 4K ones
LibreELEC Version: LibreELEC-Generic.x86_64-11.0.3
Good Afternoon LibreELEC Forums,
I had Kodi installed on this PC running Windows 10. I was able to play videos fine in 4K.
However, when I reimaged this machine to LibreELEC (i wanted a dedicated Kodi box) the 4K videos buffer a bit every few seconds. and, even after clicking the pause button the film is still playing except slowly(paused).. audio stops though. Another weird thing is half way through any 4K video the video goes green. I've tried several different movies, tv shows, Apps etc.. and it's only happening on this LibreELEC box. Also, the cache in the top right hand corner keeps going from 0% to 100% immediately over and over. Anyone know what I can do?
Internet Speed Test from LibreELEC (340 Mbps Down / 75 Mbps Up)
Specs
i3
Nvidia MX550
16GB DDR3 Ram
256GB SSD
Thank you!
