Those Omron sensors are known for going bad, sometimes if you clean the
chips off them they work. Also sometimes you can adjust the cam closer
if they get a bit weak. Another test, if Yasnac, you may get lucky and find
the bit on the DGN page to see if its functioning. There also is a final reference
pulse in the axis encoder that sometimes needs to be adjusted by a tech.
If older Yasnac, I may be able to find the DGN bit location you can check