SMEG SE335SS/1 timer

Hello

One of my friends had an issue with the oven not heating, I duly changed the oven element that had clearly blown and everything is now ok on that front. The problem is before this was done the timer control knob worked fine but now when you turn the old style control knob to set the timer it just clicks and won’t set to an actual time. When we turned the oven on it’s face to fix the element this knob did fall off but we put it back onto the shaft no problem and the plastic knob looked undamaged. Does anyone have any idea why this may be, I can’t see how changing the element would make the timer misbehave? Many thanks in advance for any help offered.