So after some research of trying to fix this bug:
https://imgur.com/a/JO5xiSu
Which I covered in this thread:
https://forums.nexusmods.com/topic/13498193-weapontexture-jitter-on-certain-weapons-during-ads/
I believe I have found a solution.
This Fallout NV mod shows the exact same issue, and fixes it - so I would assume it is some kind of engine issue? I'm sure someone with better understanding could explain it.
https://www.nexusmods.com/newvegas/mods/84443?tab=description&BH=0
To paraphrase the mod author, the 'Viewmodel suffers from floating point precision loss. The further you go away from the center of the world and look in certain directions, your Viewmodel will shake uncontrollably, jumping in places due to running out of decimal places.'
Is anyone able to replicate this fix in Starfield?
Here's a video of the bug in Fallout NV as well as the fix: