Hi there,
I am having exactly the same problem with Store app. It opens to a white window. I have tried the above suggestion but same thing.
One thing to note is that the PC has been updated with the new Windows update KB2919355. If possible I would like to keep using ModernMix but unless these issues are resolved, I am afaid I would have to remve it for now as I fear that there are other apps that may exhibit the same issues.