www doesn't work on ios Unity5.3.4

Same code works fine at Unity5.1.3 but not at Unity5.3.4

Same url same code same computer, Just diffrent version of Unity.

I rebuild all assetbundle at every version Editor.

I put all my assetbundle to streamingassets folder.

www.error always null, and isDone never goes true.

Not all www not working, only a part. Such as when I load 100 AssetBundles, 30 of them load succeed, others just never done. Work fine at windows, android, mac os, only not at IOS.

This is a every time issue, Please take a look.