Hey there, can you tell us more about your project? What did you use to record the clips that you're editing? Does it have a lot of text or motion graphics?
Rush is (obviously) getting stuck on something that it doesn't want to render. My guess is that it's probably a motion graphics template or a color adjustment or something that requires a lot of processing power.
It could also be that there isn't enough space on your iPad for this video to export! I would try clearing out the "Recently Deleted" section of your Photos app on your iPad, that always clears up a lot of space for me.
Let us know what types of effects you have applied to your project, or if it helps after clearing extra space.