Yeah like the title says, it's a weird bug with the latest version of the mod (v0.2.10.16) where salvaged parts aren't dropped by Cyberzombies and don't exist in JEI.

I'm in a custom modpack I made, and there's no config option to toggle them on or off.

What's up with this?

Also, I'm on Minecraft 1.12.2

As of 0.2.10.15, salvaged parts were only visible in the creative tab through the toggle buttons, they were not visible in JEI.
As of 0.2.10.16, salvaged parts are no longer visible anywhere. Zombies are dropping manufactured parts.
I'm tempted to ditch that creative menu hack for something more JEI friendly.

Fixed in dev, will be in next official release