Most Annoying bug in the Editor!

Whenever I import more than one Unity's standard packages which I downloaded from official website, Unity crashes. When I import Character Controller then I can't import any other package such as Vehicles one. I don't know what's the error causing this! I checked that, "Did I downloaded the packages for same version as I have?" But I downloaded the correct ones.

Now when I opened the same project that caused Unity to crash after importing two packages, this error was shown in the console:
"A default asset was created for 'Assets/Standard Assets/Characters/ThirdPersonCharacter/Textures/EthanOcclusion.png' because the asset importer crashed on it last time.You can select the asset and use the 'Assets -> Reimport' menu command to try importing it again, or you can replace the asset and it will auto import again."

I have Unity 5.6.7.f1 Personal. I have tried to report this bug to Unity team but they didn't helped.
Any help to solve this issue will be really appreciated as this problem is starting annoy me.

 

The same problem occurred in 2018.3.2f1 version, When I use "AssetDatabase.Refresh()" in "OnPostprocessModel()" function

 

Happening to me in 2019.4.6, 2019.4.0, 2019.3.6