Interesting .
Just had a look at the manual and J905 pin 5 is Upper Left Flipper Opto and J906 pin 5 is upper left flipper EOS (these are part of the Flipper grounded switches)  (page 3-2 in Game wiring and schematics section)
 
I know Creech is a 2 flipper game but the boardset and loom is common to a number of games .. so maybe you have an intermittent short somewhere in the loom causing this error ???