Could it be the 4K video is HEVC H.265 or VP9?
Limitations
- VC-1/H.264/Blu-ray format playback in the Essential version is limited to systems with hardware acceleration.
- Does not support the playback of HEVC/H.265/VP9/Ultra HD Blu-ray/HDR Video content.
- Does not support the playback of CPRM/DTCP-IP protected content.
- Does not support CD audio ripping.
- Does not support DSD audio.
- Does not support TrueTheater HDR.
- Does not support HEIF/HEIC photo file.
- A CyberLink account is required.
- Video playback quality to media casting devices may be reduced due to hardware encoding limitations.
Source:
https://www.cyberlink.com/downloads/trials/powerdvd-ultra/download_en_US.html
Dave