I see two areas to concentrate on...

1) The 7th digit is not working on any of the displays when all Pinscore. I'm wondering if there is an issue with the daisy chained pin 12 harness as this is the control line for this digit. A marginal issue that the Pinscore displays cannot handle as well.
2) The issue gets worse with displays further down the daisy chain. Evident with the last two daisy chained displays (P2 and P4) stuck at zero. I wonder if you remove just Pinscore at P4, will that also produce correct remaining displays (same response as removing P3)? This would point to a loading issue due to poor connection within the harness (probably pin 12 again). One of the wire to connector interfaces may have many wire strands broke or oxidized. I'd try running a jumper wire from Pin 12 on P3 (first in the chain) to pin 12 on P4 (last in the chain) gets rid of the issue.