novusun NCH02 - F goes to zero with no reason

HI,
I'm experiencing a strange problem with novusun NCH02-NCD02 controller.

In the middle of the part program (around line 5000 of 13000) the axis do not move (the spindle continues to rotate)
and on the display the message is "SYSTEM IS RUNNING" while the real time feed goes to zero.

Please see the photo attached.

I checked the part program generated by Fusion 360 but I didn't see anything that could reduce the feed to zero.

Thanks for any help