Parent page won't scroll once reaching end of iFrame (iOS)

I created an Ionic App that I am serving across a few places via an iFrame. (Ionic 4)

Once reaching the end of the iframe scrolling, the parent page does NOT scroll for iPhones or iPads in Safari or Chrome. It does work for Android Phones and Windows/Mac desktop.

(I know iOS has some issues with scrolling of parent which can be resolved by setting -webkit-overflow-scrolling:touch in the parent div, but it does not work with this case.)

Does anyone know the class responsible for preventing the parent page from scrolling?

Everywhere there is overscroll-behavior:contain I have replaced with overscroll-behavior: auto with no luck.

I want to leave a note here for any other devs who stumble upon this.

We were able to “solve” this issue with our web app by disabling y-scroll and implementing the iframe-resizer library (available on Github and NPM).

So there is no need for internal iFrame scrolling since the iframe height is adjusted automatically with that library when the app content changes and/or the window shrinks or expands. This resolves the non-parent scrolling for iOS.

Obviously still interested in knowing what is blocking iOS parent scroll with iFrames with Ionic if anyone may know.