HEVC 4k stuttering

Hey guys, bit puzzling, but I’ve downloaded some files in 4k and for the first time (I’ve been playing a large number of 4k files with no issues) I’ve had stuttering issues. I’ve got an i5-4460,16 gb DDR3 and a GTX 980 so clearly not a lack of power.

I’ve had a look at the codec and it’s HEVC. Done a bit of Googling, seems to be a problem a few people have had. If I play the file in Kodi I get stuttering. In VLC there’s stuttering, as well as that weird grey wash over everything then back to stuttering.

I’ve verified the issue isn’t the files by playing the directly through the PC.

Any ideas?