de Broglie standing waves are waves that represent the probability of finding an electron somewhere. In an atom, these waves must become standing waves in order to ensure that no destructive interference occurs which would mean that the electron probability would become 0, hence not existing at that particular energy level.
Because it is completely flat, that must mean the total sum of probabilities of finding the electron is 0 everywhere for an instant. Thus for an instant, the electron of an atom must not exist? This doesn't sound right so what actually happens?