Slam tilts don't reset the game, they just end the game in progress. In switch test mode, though, a slam tilt is a closing of a switch just like any other.
What happens in switch test. If you see the slam tilt switch closing, then there's a switch problem.
If the game resets, then your issue has nothing to do with 'slam tilt', and it's just a typical WPC reset problem.
I'm leaning toward the latter.