Update: It seems that it has to do with me using a new Mac. There are quite some people around the net who do have the same issue, e. g. “I don’t know if this is helpful, but as I have a bootcamp partition, I’m able to verify that on the exact same hardware, using a texture to drive volumetric density in eevee causes the volume to disappear on macOS Mojave, but works as expected on windows 10.“
