Silyavski, I'm having similar issues, maybe my basic explanation will help if my problem can cast a common light on the issues?

I have 2 NPN proximity switches, each a 3 wire switch.

I set up a simple bench test with a 12v PSU and connected proximity switch brown to +ve and proximity blue to -ve then I used a simple continuity tester across the proximity black and brown.
As the proximity senses a metal target, the continuity test works as I would expect.

Then I set up Mach and the inputs so that I can see the BOB inputs are working on the Mach diagnostics screen.

Also the proximity switches light up with thier little LED, they work with a continuity test.

BUT when I connect a -24ve to the proximity switch and the Bob on one pin, and the poximity black to the other Bob pin, nothing happens in Mach.

Any ideas?