You've gotten all your layouts and event sheets confused! You should give them appropriate names to make it clearer (not just layout X events).
On the layout 'Level 3' - the one which isn't working - check its properties (click an empty space in the layout or select it in the project bar). The 'event sheet' property is set to 'Layout 6 events'. If you look at the event sheet 'Layout 6 events', all it contains is an event to set Text3's text. So the collision event isn't even tested for Level 3!
'Layout 4 events' contains something like what you want, but it tests for a collision with Sprite7. The spikes in Level 3 are called Sprite3.
You should keep your project organised to avoid problems like this. Firstly, give everything proper names (objects, layouts and event sheets). Secondly, copy and paste the same object between layouts so you dont have multiple objects which look the same but are different (eg Sprite3, Sprite7 - confusing huh?). Finally, I'd make sure every layout has its own event sheet, and use a separate event sheet for common events (like for showing how many lives you have left). Add the event sheet in application properties, and in each layout that needs those events, add an Include in the layout's event sheets. That way, you shouldn't get confused with which layout is using which events.