Your comments

Spot on. Once the external keyboard was deactivated and a new file was created the issue disappeared. Lines 1 & 2 are now clearly visible.

I can no longer reproduce the issue (even with external keyboard re-activated).

Solution appears to be to temporarily disconnect external keyboard during use.

I've noticed similar behaviour on my iPad Mini (w/Retina). When opening a new file the first two lines are obscured by the context bar at the top of the screen.

Dragging the page down temporarily shows the top of the file until you let go, then it automatically slides back under the top bar.

Pinching and zooming out exacerbates the problem. Zooming in brings it into view but makes the application somewhat unusable.

Workaround is to start a file on line 3 (hit return twice when creating a new file). No biggie, just mildly annoying.