Replace both capacitors C20 and C21 at the CPU board (1uF ceramic). They tend to loose their capacity over the years narrowing the Watchdog window. This watchdog is monitoring "keep alive signals". If these are not coming fast enough the watchdog kicks in resetting the game. The revision 5 game software is just speeding up the keep alive signals. The real problem are the capacitors and sometimes the 74HC123 (but rarely).