I feel this may be a bug related to the canvas element or the way it is repainted (when control comes to that view (I mean page) after going to some other view) when the view is re-rendered, please correct me if this is wrong based on the description.
This bug appears to be a generic one observed on iOS 14 & above on both iPhone and iPAD. The bug does not appear till iOS 13.6 (verified on iPAD Air 2019 iOS v13.6)
The bug is as follows:
The view elements (say text box, input .. esp those at the top) are rendered correctly when the user visits a page first time (e.g. as in goes from page 1 to page 2, then the view elements in page 2 are rendered correctly). Now if the user goes back from page 2 to page 1 & then revisits page 2, the view elements (esp those at the top) disappear.
The following video clips can help understand this better:
#1 2 mins: https://drive.google.com/file/d/1ycO3YcJeSMA8kmDm6g9ciLUdbEQ-TNbC/view?usp=sharing
#2 Less than 25 secs : https://drive.google.com/file/d/1bUBkHQaC0bn6FofLZz2KXTRTg78rF0mx/view?usp=sharing
(Please look at both clips)
Now if one were to pull and drag down the screen/canvas area at the place where these view elements were originally, then the view elements show up (it's just that they have somehow "gone over the top" after we want back to the earlier page) look at this video clip https://drive.google.com/file/d/1LKYkqNRrDIE2-f61amMu_gv2QK8lNQf-/view?usp=sharing
This bug has been observed in the "HTR Resistor Finder" app using Sencha Touch/Cordova (App store link: https://apps.apple.com/us/app/htr-resistor-finder/id923363496 ).
The app has worked perfectly well iOS 7 onwards till iOS 13.6 as also it's working well in all versions of Android 4 onwards till 11, that is the latest Android version.
The bug appears to have been introduced due to changes in Webkit in iOS 14 onwards.