MV-ELA Marquee lights driver issue

Sometimes what seems to be easily fixable turns out to be a little more complicated.

I've got a problem with the marquee lights on my 6 slot: EL panels light up in order 1, 3, 2, 4, 5, 1 instead of 1, 2, 3, 4, 5, 6 in the hardware test.

There are only 4 ICs on the board and I've fully tested the 74LS138 & 74LS368 and can confirm they are fully working.
Other ICs are a 74HC132 and 74HC174.

I've clearly identified that signals A2/A1/A0 coming out the 74HC174 are wrong.

It should be:
A2 - A1 - A0
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1

Instead I got:
A2 - A1 - A0
0 0 0
0 1 0
0 0 1
0 1 1
1 0 0
0 0 0

Which explains the 1, 3, 2, 4, 5, 1 cycle...

Other info:
CLK signal (pin 9 of the 74HC132 going to pin 9 of 74HC174) is just the CLK signal on pin 3 coming from the MVS board which is Schmitt triggered NAND 2 times in a row so is basically the same signal than the one coming from the MVS board but Schmitt triggered.
/MR signal (reset when low) is a Schmitt triggered NAND 2 times in a row of signals /O6 & /O7 so basically a Schmitt triggered AND of /O6 & /O7 (makes sense since those signals are low during the 1, 2, 3, 4, 5, 6 cycle and goes high one after each other for 7 and 8).

So any idea? Seen this before?
I could simply swap the 74HC132 and 74HC174 but I'd like to understand what is the issue and how to diagnose it.

Fixed: was a bad 74HC132.