Cursor moves outside text field - iOS Safari

The cursor doesn't stay in the text field when you scroll up and down if the text field is in a fixed position container. See videos below.


Abercrombie

https://www.abercrombie.com

Video: https://www.dropbox.com/s/8w0gft6z3swv8a5/Abercrombie%20Position%20Fixed%20Container.mov?dl=0


Development Webpage

https://webchat-dev.blueroos.com/162248887705937

Video: https://www.dropbox.com/s/ychvmztac72hqrc/Last%20frame%20shows%20tappable%20area.mov?dl=0


You have to click twice to make the cursor show up, and when it does show up, you can move it up/down using scroll on the page. Also, the tappable area for the submit icon on the right moves up/down too, so you can't tap on the submit icon anymore.


Any thoughts on workarounds?