If I tap the rightmost key of the onscreen keyboard, the note is triggered only when you press the left side of it (the green area shown below).
If I press the right side (the red area), it does nothing.
this is some hw limitation of iPhone, i noticed same "non-responsible" area in other apps too... for example in Model D almost whole most right key doesn't react
(i have iPhone 6S)
Now I look more, it does affect the XY pad above, the record button, etc, and it always affects that side of the UI. It is still the right-most key, the XY pad, etc, when the iPhone is rotated.
I hope to get an iPhone 11 Pro this week (the battery on my ancient 6 only lasted 3 hours while playing with NS2 this morning), so I'll see if it's better after that.