modlist
__MixinBootstrap-1.1.0
ForgeRocks-7.3.1-1.12.2-full
fp2-0.0.1.728-1.12.2
Default Settings
screenshots:

Still issue, though interesting thing is that when items are being picked up (as soon as they fly towards you), they become normal looking
Edit:
Also the darker texture is the more transparent it is
Edit 2:
Also relevant for items held by mobs

But not at a distance

I have been trying snapshot versions which all run into this issue, but the "stable" that I run on my personal modpack is 0.0.1.617. I haven't updated past that for stable stuff but I do check out newer builds to see what could be.

This is especially noticable with the Real First Person mods. Unfortunately I haven't tried it without all the mods so I had no idea if this happened with no mods touching anything relevant. I've been staying on older versions for now and only trying newer versions to see if they crash or not.

@DoomRater which ver do you use?