Does the machine have a dual wound spindle motor? If so check the winding contactor for proper operation
Also,
Look at G21.1 and .2 in the ladder.
both off indicates gear 1 parameter 3741
G21.1 on and G21.2 off indicates (should indicate) gear 2 parameter 3742
Check the above parameters as well as parameter 4020 the ensure they haven't been inadvertently changed.
Also try with the spindle override at 50%. Does the speed register at 250 or 440 rpm?
Look at the spindle information under the System area. Observe the spindle tuning and setting screens and see if anything there points to an issue.