In the end, the main issue I had was with iOS Webview (both UI and WK) and iOS Safari. If you had an input within an iframe and then tapped out of that iframe. Whenever you tapped anywhere, the keyboard kept re-appearing even when you closed it again by pressing Done.
To resolve this I added a hidden input field (set the height to 0) and set focus onto this input field, whenever the user left the page that the iframe was on in the ionViewWillLeave function. Standard inputs once focused do not have the same issues as iframe inputs.
Hacky solution I know - but seemed the only way to resolve.