When ever I'm far back enough in this tunnel, the sky outside goes black until I go back within about 10 blocks of the door, I don't have any mods that change the skybox or anything that I think could be messing with it. I tested it with other shaders and Bliss is the only one that does this.

this is "cave fog" blotting out the sky in low sky light level. you can disable it in shader settings -> fog settings -> cave fog