Build a wall with theese and you'll see
Edited: other blocks seems dont have that problem
Version: nightly-dc995e9
dynamiclightsreforged-1.18.2_v1.3.3
rubidium_extras-1.18.2_v1.3.1
rubidium-0.5.2a

Actually, I've noticed lighting erros with a multitude of my other blocks, so I'll try to remedy those as much as possible

I've noticed this with the cast iron sliding breech as well - it's more subtle due to the black color.

I believe it has to do with Minecraft's lighting engine and its limitations with custom models. You could try using Forge's experimental lighting option, which can be turned on jn forge-config.toml, but I'm not sure if that will completely fix it, especially on contraptions.