PREFIX: "Solved" at the end
Thanks for the analysis Pango.
I was able to split the colors the way u did and I saw the same thing.
So I went thru other images:
NPCs - 2 Npcs Ive tried were clean, with black background where the alpha is.
paperdoll weapons - they are messy when split. And dont have these issues ingame (but indeed they are in the inventory and not placed about the 3d scene like handheld)
MOBs - clean.
Commoners were not so clean, but not as messed up as 1st person handheld.
Than I tried my
horse, its completelly messed up when split, and looks ok ingame TO ME. And thats technically a hand held..
The 1st person handheld based on Megaten work (which I built upon) are different when split and thats a fact, good catch on that. The weapons I created on my own like staff or bows are clean. BUT speaking of bows, there is a report with a bow, image in the OP - so I split the bow and its - CLEAN
This leads me to the direction of thinking, this might not be the root case after all... because the frames of bugged bow displayed in the OP are clean when split, Im sure about it. Those are the still frames - when u just hold the weapon in your hand. Thats why it was reported to me, because the user uses bows a lot, and noticed this when equipping the weapon... and for him, once seen, cannot be unseen and became very distracting..
EDIT:
Was able to replicate the bow bug, thats good! And with some tunning of reshade to brightnen up the scene, I can now see the bugs on swords, when u swing it, it creates lines across the whole screen :X Damn
EDIT 2: "solved"
So I tried changing some stuff around in inspector, texture wrap did nothing, but when I switched texture compression quality from very high (BC7) back to normal (DXT5) the lines on the bow dissappeared
And I guess "thats it" because what else can I do?