The Tapioca Pudding Problem was first articulated by C.S. Lewis in an interview with Time Magazine in 1947. While discussing the idea of trying to think of God in non-anthropomorphic terms, he related a story of a friend of his, who, raised with seemingly critical spiritual beliefs, and with the idea of God as a substance, just pictured God as a gigantic ocean of tapioca pudding.
While that might be a somewhat silly exaggeration, it is true that attempts to de-anthropomorphize concepts, theological or philosophical, just replaces them with another concept, which is equally literal, just in a different direction. If we accept that a human soul is not this Casper the Friendly Ghost blob of ectoplasm that is inside of us, what is it? Other options can include: a luminous field of glowing mist, a rotating tesseract, the spirals that form when we rub our eyes really hard, a wire frame in bright colors, or a Steve Ditko landscape with pathways between floating eyes. Basically, any attempt to remove anthropomorphic concepts from questions like "What is God like?" or "What am I like?" is going to just run into some type of mystical imagery that looks like either a trapper keeper from the 1980s or someone's community college 3D design class from 2003 where they got a B- for effort.
This does present a problem, because a large part of our continued need to mature is to realize we have a self beneath our changing, surface features. But when we try to imagine what that non-tangible self is, what do we find? Often, we try to imagine a bowl of tapioca pudding, or the equivalent.