Ive been experiencing the same issues. Pushing a update to preview it on the iPad will not always load properly, or not load at all. Quitting the app seems to work and have updates come through but not every time. Ive seen a few other threads on this issue so your not the only one.
Its now working. Got the preview to work by adding a new piece of metadata - and then the preview showed up on the phone after two hours. Then deleted the extra metadata! Seems like preview commands need 'flushing' through - does that ring any bells with anyone else on here?