Entites do not render behind translucent custom entity

I tried to make windows you can look through for some custom entites.
The "slime_outer" material seems to work in the first place but when viewing through the glass or going in a different viewers perspective when sitting inside, makes other entites invisible which do not have the "slime_outer" material (custom and vanilla) -> slime and other custom entites with the "slime_outer" material are visible.