Hi @sam_nazarko
I did a little googling and found folks over on coreelec reporting the same problem as me:
as mentioned there: “The shaking seems to happen only when video resolution is = display resolution and video is interlaced.”
I tried their suggested workaround of setting the zoom amount to 0.99 (set as default for all media) and low and behold the issue is gone.
Would be nice to fix it properly as i do now have a small black border, but can certainly live with it for the time being.