Unity WebGL in ios, loading but not complete

Hi, I am trying to build my Unity WebGL and use IIS to share through the Internet. I've successfully implemented on PC and Android(Android8.0.0⩓roid7.1.1, using native browser, chrome, firefox). They could open WebGL in a minute.

But when it comes to IOS, WebGL could be loaded using Safari and Chrome without any warning, but it couldn't finish loading in ten or even more minutes, just as the picture shows. I've tried IPhone7P&IPad mini2 with IOS12, IPhone7p with IOS11. What should I do?