How to reproduce:
1. Create a new Unity project
2. In the Hierarchy create a new Sphere GameObject
3. Select the Sphere GameObject and attach a Cloth component to it via the Inspector
4. In the Sphere's Transform component change its Scale to 5-5-5
5. In the Sphere's Cloth component click on the "Edit cloth constraints" button
6. In the Cloth Constraints window set the Brush Radius to 1
7. In the Scene view draw on the Sphere

Expected results: Drawing on the Sphere changes the Constrains that are on it
Actual results: Drawing on the Sphere doesn't change any Constrains that are on it

Reproducible with: 2019.3.0a7, 2019.4.26f1, 2020.3.10f1, 2021.1.9f1, 2021.2.0a17
Not reproducible with: 2018.4.35f1, 2019.3.0a6
Could not test with: 2021.2.0a18 (Unity crashes after step 3)

Note:
-In the 4th step, the Scale needs to be numbers bigger than 1-1-1
-In the 6th step, having the Radius set to 2 and drawing on the Sphere changes the Constrains seemingly at random
-In the results section the Constrains that are on the Sphere are indicated by the black dots that are on it
-If the Paint tool Brush Radius is bigger than the GameObject size the tool works as expected