I'm using Antique Atlas Version 7.0.3 on Minecraft 1.18.2 and Forge 40.1.84.
As soon as shaders are activated the handheld antique atlas is getting some unwanted transparencies.
I experienced the problem with different shaders while using Rubidium and Oculus.
Turning several options on/off on the video settings/shaderpack options didn't help.

Mostly the same issue like #416

which shader are you using? BSL and Sildurs Vibrant work fine for me.

I also got the problem with BSL