Calculated field doesnt show value until restarted

[Khushalay]

I have a calculated field on the form, it was working fine till now but since last two days, it shows zero until I close the form and re open it. Shows the correct value only when its restarted.

What could be the issue?

It was working very well till yesterday and I haven't done anything to the coding or designing.

 

[Khushalay]

Actually, the field is not calculated but a normal number field. Another field's on click event would update this field.
It used to show the proper result/figures till yesterday but now it only updates after the form restarts.