I encountered this bug some days ago and first me and GM Foxy thought it was due to the candle being too far on the edge of the platform. However, it seems to be the case that the candle mobs don't spawn when you leave the map (and presumably when no other player is in the map) before they spawn. I believe this is pretty much an edge case. It only happened to me because I find it easier to spawn the candles by killing the cakes with my NL rather than with my mage. On top, you'll have to be quick with leaving the map, otherwise they'll have spawned already. I Flash Jumped out of the map to continue doing the other stages and return with my mage, to only find 20 candles/apples and unable to finish. On the screenshots you can see that I killed both cakes, I am outside the stage map with only 1 spawn notice and finally only 9 candles at the bottom where there should be 14. I know the screenshots aren't conclusive, but sadly I don't have an app to record my screen.