Preview functionality within Hype. No particular types of assets. Will check exports each time from this point on to check that side of the problem. My memory is not serving me well on that question, but I think there was no problem on the export side.
One thing I have seen before; when a document is worked on for a long period of time in many iterations, as this one has because of client changes etc. there seems to be a tendency toward corruption of data. I am going to copy everything over to a new Hype file and see if the problems follow. Past experience with other documents saysl that often fixes similar issues.
I am also sequestering iCloud as much as possible because I am certain there is a problem there, I can't help but think that iCloud interferes with more things than we realize, but thats another story.
Will let you know in a day or two.