How to reproduce:
1. Open the attached "imgui-bug-master.zip" Unity project
2. Build the "SampleScene" Scene for iOS
3. Run the build on an iOS device and tap the 3 buttons

Expected results: each button's icon visually changes to its own active state when clicked
Actual results: only the first button's state changes when any of the 3 buttons are clicked

Reproducible with: 2018.4.6f1, 2018.4.15f1
Not reproducible with: 2017.4.35f1, 2018.4.5f1, 2019.2.16f1, 2019.3.0f3, 2020.1.0a17

Notes:
1. Tapping does not visually change buttons which are not located in the (0, 0) coordinates
2. The button taps are registered, but their visuals do not change to indicate the pressed-down state feedback to the user
3. If more than one button is present and one of them is in the (0, 0) coordinate, every other button tapped will visually change the upper left button's visual state

Reproduced with:
iPhone 8 (iOS 11.0.1)
iPhone 8 Plus (iOS 12.1.2)
iPhone 11 (iOS 13.0)