Touch target sizes are recommended to be at least 44 x 44 points. Buttons in the navigation bar ( especially when not using nav bar button items), dismiss buttons, and custom toolbars, are use cases that tend to have smaller sizes.

Calendar of Advent of iOS Accessibility. Day 15. Small touch target sizes. Three examples of common cases with buttons that tend to have small touch target areas. The first one is buttons in the navigation bar. The second one is dismiss buttons for modal or inline popups. The third one is toolbars, especially custom ones.