At the heart of our modular digital board game system is a parallel-in-serial-out shift register. But our earlier board design completely missed out the fundamental part that made the whole thing work: daisy-chaining shift registers is achieved by connecting the Q7 pin on one to the DS (serial data) pin on the next.
And we'd completely forgotten to connect the Q7 pin to our ribbon connector!
Here's the new PCB layout with the extra pin connected (there's probably a neater way to do this, without having to cross the traces over each other with 0ohm resistors but without a complete re-write, this is next best thing!)
Our ribbon connector is now a 7-way plug. We've drawn it as a dual-row 10-way IDC connector only because these tend to be quite common in the "real world" and are more easily sourced (and cheaper too) than lower pin-count connectors.