I have had situations where there was a fault with the one player display and it caused problems with both player one and two.

+1 i have come across this several times, where a fault in one of the display glasses causes segments to go out in other displays. Had that problem on my Flash when i got it up and running.. segments out on the master display and players 1 and 2. It ended up being a bad display glass on the master display itsself causing the problem.

Havent seen the all 8s fault before though, that a new one to me   I would still try beaky's suggestion for the 3 and 4 player displays as well. could possibly be a bad glass affecting the other