Fixed Header moves bizarrely when I click a Select2 w/ search functionality on IOS 9.3

I have a page with a Header (styled with Position: Fixed) and a few Select2 w/ search functionality components.

When testing my page on an iPad with iOS 9.3 the Header moves from the top, to the bottom of the screen then moves back to the top.

I have some Select2 components without the search feature and they do not affect the positioning of the Header.

I want to keep the search feature, what could be the issue?

Any possible information or solutions to try would be great!

Thank you in advance.