WebGL on iOS: empty scene test build does not work on reload

Have tried a few simple projects as well as an empty scene and am experiencing the same issues with Safari and Chrome on iOS.

First load: unity loads fine (usually in about 5 seconds)
Second and subsequent loads: Hangs with loading bar at 90%, never completes.

I can replicate this every time on an iPhone by restarting the app / flushing browser cache.

Any ideas what might be causing this?

Thanks!

 

I just noticed the other "optimizing load times" post *also* mentions mobile reload problems:
https://forum.unity.com/threads/optimized-webgl-load-times.554479/