I know this was an old question, But for anyone come here because they are having the same issue, I am adding my solution here.

It doesn't even have to be at the bottom, but I had some pages with an Entry field and a couple of buttons which had the same issue (Button clicks won't respond on iOS devices and sometimes even you can't type anything on Entry fields)). Tried lot of things but nothing worked (VS for Mac). The only solution worked for me is to replace the VerticalStackLayout with a GridView.

May not be a solution for everyone, but if it fits you, works perfectly.