Probable issue with 74HC595 not outputting ANY data
It turns out when translating the datasheet from Chinese with the Google translate app, the opening paragraph says &quot;There are storage registers and low-level and high-impedance outputs&quot;... They're open-drain outputs, not tri-state... Not all parts are created equal it seems...
For anyone curious and in need of an open-drain 74HC595, the exact part is here.