HEVC Playback awful???

I have several mkv & mp4 files that are encoded to the 1080p HEVC x265 standard that I have added in to my kodi library.
I am now using a minix Z83-4 htpc windows 10 box as my HTPC.

The problem is, when I play these HEVC x265 video files in Kodi 17.3, they’re jumpy, robotic-like.

But … when I play the same video files back in Windows media player or the windows film & tv app, they play brilliantly, nice and smooth.

I’ve tried changing the video acceleration and the post processing settings and nothing seems to work.

I cannot understand why playback is crisp and smooth in windows, but dreadful in Kodi.

Any help here would be greatly appreciated as it’s a real pain to have to keep switching between kodi and windows.