Not for sure. Deleting cells can make the cells underneath rise up one to replace the deleted ones, which can make all sorts of problems if you are not aware and compensate for it. Make sure you are not using delete when you wanted clear.
As for entries being lost, difficult to know why, unless the values it was calculating with had been deleted, causing the cell somehow to become blank. But usually if data is unavaiiable you get an error message in the cell instead.