Steps to reproduce:
1. Download and open project "Minegur.zip"
2. Open scene "MinegurScene"
3. Enter play mode
4. Click "Start/Stop mining" button
5. Exit play mode & enter play mode again

Actual result:
Unity editor crashes at "GameObject::IsActive" in Retriever.cs line 63 "r = UnityWebRequest.GetTexture(imgStruct.data.link);".

Expected result:
Playing the scene second time without crash.

Notes:
Stack traces are different in each tested version. Look at attached logs.

Reproduced with: 5.2.4f1 (sometimes, but not always), 5.3.4p1, 5.4.0b11