EDIT - This is for the S3. The Nomad apparently has a bottom fixed nut.
The AB nut has two halves. The top half should NOT be loose, it should be fastened to the Z Carriage with 2 bolts.
The bottom half is ‘floating’. It will appear loose, but it will not rotate too much simply because it is too wide. This is normal.
If the top half of the AB nut is fastened to the Z carriage, but appears to be loose on the screw threads, then your nut is worn, and may need replacement. If so, contact support - the nut is not available in the store.
https://community.carbide3d.com/t/z-plus-leadscrew-nut-replacement-how-to-guide/53601/4