Closing, as this Unity version will no longer be getting updates.
Fixed in: 2022.3.23f1
Fixed in: 2021.3.37f1
How to reproduce:
1. Open the user’s attached “unity object pool error.zip” project
2. Enter Play Mode
3. In the Hierarchy, select “ObjectPoolTester” GameObject
4. In the Inspector window, press the “Pull from pool” button 11 times
5. Press the “Return from pool” button 11 times
6. Observe the “Active objects” number under the “According to ObjectPool” text
Expected result: Number is 0
Actual result: Number is 1