Random pixelation after zooming frame

I Am at quite an advanced stage on a Prezi and have quite a large amount of graphics loaded, PDF, JPEG and PNG, and was playing really well. At about 12.30 today (GMT) I expanded the main frame of the Prezi, that contained all the content and found that much of the graphics started pixelating, but randomly ( ie if I clouded Prezi the opened again and presented again, different content would be pixelated.

Have tried shrinking the frame again, but still get random items corrupted, but on subsequent run throughs correcting itself.

Whatever I do, cannot get it presenting properly all the way through. Is there a fix for this, or can the Prezi be reverted back to a version from earlier in day?
Any help appreciated as have spent a couple of days on this.

Thanks,

Paul