Rekordbox dvs calibration issue with 1 headshell, not the other

I have 2 turntables with different headshells on each. On the one with a Stanton headshell calibration works OK, on the other ( "GT") I just get a straight-line in the calibration window, and nothing plays.

Can confirm it's a headshell issue because if I swap them the problem swaps too.

The problem needle is a cheap one, but it does play vinyl in normal phono mode just fine.

Any idea what the problem could be?