Help with cubemap rendering!

[finite basin]

(notice the Slice/Face dropdown!)

But later during the frame, when I try to sample the cubemap, it looks like this:

(notice that the TexEnvCube does not look at all as expected)

When sampling in the shader, it seems like it always returns black (0, 0, 0). The sample code looks like this:
Output.rgb = texture(TexEnvCube, NormalizedDirection).rgb;

Does anyone know what might be wrong here? Maybe someone here has a bit more experience with cubemap rendering in raylib?