Checkbox group bug

I’m using the free version v. 2.5.8. Using “Checkbox group” form with four items, there’s a bug when trying to select an item. This only happens on my mobile (iPhone 7).

In portrait mode I’m only able to select the first item, e.g. checkbox is green. I’m not able to select item 2, 3 and 4, visually that is, because if I flip the phone to landscape mode, the item visually not selected in portrait mode is now selected indicated by the green checkbox. Turning the phone back to portrait mode and all items are suddenly selectable.