Steps to Reproduce:
1. Create a UI Widget 2. Add a Checkbox 3. Scale Checkbox: Details > Render Transform > Transform > Scale > Set X and Y to 3.5 4. Run Game From Editor (PIE or Standalone) 5. Hover mouse over various points in the checkbox while clicking
The mouse only fires an event in a small area of the scaled checkbox (top right).
It seems that the mouse target area did not scale with the boundaries of the checkbox.