How are pins 1 and 4 in terms of DC voltage on the octal socket? With the bottom panel painted, you may have an issue where those are not being properly grounded.
Also, photos of the tops of the two PC boards could help, just to check the parts themselves.
From what I see, the C4S loads on each 4P1L are working OK, and it appears that the TL431 is receiving power, but not regulating. The high voltage at each Kreg makes me wonder about swapped R1 resistors or a grounding issue at the octal socket.