When collecting or editing a feature in Collector, when you have the pop-up window open, a narrow strip of map between the pop-up and the Submit button (or Update button when editing) remains active. If your finger misses the Submit button you end up relocating the feature you are collecting to this almost hidden strip of map. I suggest either making the pop-up window be flush with the Submit button, or making this thin strip of map inactive and un-clickable. As the user interface is currently designed, it is too easy to accidentally relocate a feature, especially if you are collecting a point feature. There is also no utility in allowing a feature to be relocated behind a pop-up window.
I attached a screenshot of a point accidentally relocated to this strip just below the Submit button, marked with a yellow arrow. The original location of the point was in between the two blue points visible on the aerial photo.