Ryzen 2700x 4.1Ghz all cores, RoG Crosshair 7 Hero Wi-Fi, 32GB 3000mhz C15 ram with RX 470 8GB GDDR5.
Issue is after gaming, or after a session of using Windows RDP - the graphics card seems to bug out. This bug causes the GPU to spike to 100% usage in task manager with Video Decoding maxed when trying to view 4K .mov files.
This can be resolved by restarting computer, or disabling and enabling the GPU/Display Device in Device manager. After this, video decoding drops to 10% when viewing the 4k .mov file.
This leads me to believe some software bug causing the incorrect codec/driver to load during viewing the content.
Software used to preview is MPC-Home and similar happens with VLC media.