Why do some Chinese characters have no pronunciation, unclear meaning, no source and no use cases?

One of the reasons is related to taboos. In ancient times, there was an unwritten rule that the younger generation could not call their elders by their first names, even if they were homophonic words. For example, if someone's father's name is Li Ming (literally, don't compare it with whether it existed in ancient times), then he can't explain the words, such as name, life, ghost and so on. , even the official name! For example, his father's name is Zhang Jin, so he will never be admitted to Jinshi in his life. In order to reduce this kind of tragedy, the ancients can make strange words until they die, preferably the kind they will never use.