Seems as though your switches are all OK.
Have you done any work on the machine recently? Changed lamps for LEDs etc? Adjusted something under the playfield?
Below shows a portion of the switch matrix for MM - we can see from that you have the Slam Tilt as switch #21 and the Plumb Bob Tilt as switch #14.
The ST connects to the MPU board at connectors J206 pin 2 and J205 pin 1
The PBT connects via J206 pin 1 and J205 pin 4
The common factor here is that (as the diagram also shows) both tilt switches connect to IC #U20 - this is VERY WELL KNOWN as a failure point when people have been "playing around" under the playfield. (It also shows connection to IC U17 but this is a rare failure point unless you have tried very hard to damage it
)
You should (power switched OFF) unplug connector J206 from the MPU and turn on - if your Tilt warning remains you can bet IC U20 is knackered!
