Ironically problem seems to be sorted.
Tried a file on a usb connected to the unit, still stuttered, so got ready to get a log. Installed the log uploader, enabled debugging, restarted Vero, opened the usb file if just tried… Nothing. No stuttering at all. Oh. Then tried a file from my network drives that I’d checked literally dozens of times before and had stuttered every time. Nothing. Again, no stuttering.
Would seem my vero’s osmc is at one with progressive society and identifies as Windows, so a simple reboot fixed the issue.
Watched quite a few x265 files since with no issues.
So for me, it’s fixed at the moment.