First look for a bad escape switch (test with a ohm meter).

Next look for a wire broken off the escape switch.

Next look for bad solder joints on the coin door interface board.

Next look at the CPU board for battery leakage damage.

I just repaired an Addams Family cpu board 3 weeks ago with the same exact problem you have (also happened suddenly). It turned out to be a broken trace underneath the U16 chip. The problem was not obvious until I removed the chip and performed a trace-to-trace continuity test with my ohm meter on the component side of the board. Even under a magnifying glass the trace physically looked fine, but the meter said otherwise. So I installed an IC socket and one jumper wire to restore the circuit. Popped a new chip in the socket and tested it out. All was good to go again. Problem solved.

Sounds like the chip had gone bad. Glad you got the escape switch problem corrected.