is the game mode from the level selection screen"endless"? if yes change it to "story", you can't progress the story if the game was in endless mode.
I checked the code and I'm sure that this is the issue you have, try the level again in "story" mode and if the milk didn't appear after 5-6 minutes from running please tell me.
I just updated the game and added "explorer's mode" in the options tab, this will make you unlock all the levels. If this problem reoccurs, use it
if you are playing the downloaded windows version, redownload the game and the "explorer's mode" will appear in the options tab. don't worry about your saved progress; it will remain
