If you feel like you've upgraded everything, but the progress upgrade bar looks similar to the photo below, you'll want to check the upgrade screen for every chapter in that venue:

So while chapter 4 may show all upgrades have been purchased:

Chapter 3 shows us that Fried Chicken, which isn't used in Chapter 4, needs one more upgrade:

Once purchased, you'll be able to collect your piggy bank, as indicated by the exclamation point!