Quoted from HeyItsMeDusty:First issue: none of the pop bumpers were registering, and the bottom one would issue a tilt warning rather than firing.
I would start with a switch test. Using your switch matrix chart on page 17 in the manual and the switch matrix general troubleshooting process at the Pinwiki https://www.pinwiki.com/wiki/index.php?title=General#The_Switch_Matrix
Determine if the MPU is reading inputs correctly. If so, your issue is in the playfield.