The only way to explain one-at-a-time DSE is that each photon (or electron, neutron, buckyball etc.) does indeed interfere with itself. Nobody knows exactly how that happens, but happen it does. In a non-standard theory like de Broglie-Bohm, 'pilot waves' do the trick, but it still amounts to photon/electron/whatever self-interference.
The self-interference is occurring at the slits not at the detection screen - but the effect of self-interference gradually displays there over time. Some evidently get confused regarding the cause-effect relationship.
The self-interference is occurring at the slits not at the detection screen - but the effect of self-interference gradually displays there over time. Some evidently get confused regarding the cause-effect relationship.