Coffee Cake Crisis

The lemon loaf cake from my Dan Lepard cookbook was a great success (if rather small) but the coffee cake is a b****r. First time it was overcooked, flat and biscuit like. This time after reducing temperature and time it seemed Ok texturally but rose up in the oven then collapsed, still in the oven, 5 mins later. I think it must be the tricky mix with the veg oil and whisked egg. Do I keep making it obsessively until I crack it or should I move on? I FOLLOWED THE INSTRUCTIONS TO THE LETTER BOTH TIMES! I will fill the dents with buttercream and hope no-one notices...