Bug Texture Nulled After a while [AssetBundle]

Hello,i am getting skin textures from asset bundle,

it loads correctly at the beginning however after a while around 3-5 second my material skin textures becomes null, it looks black!

I think there is some unload issue or something else, but I never unload my assetbundles anywhere,

any help I will appreciate please watch the video!

https://www.dropbox.com/s/mafvt22unp4ejp3/assetbundle_problem.mov?dl=0


here how can I change the texture

https://capture.dropbox.com/MTJaNIYRuvggFT7n

 

Resources.UnloadUnusedAssets() function makes texture disappear loaded from asset bundle , it can be considered as bug?

I found the problem was here ;