Steps to reproduce

1. Go to discussions and tap on a discussion

Expected results

• The transition is fluid

Actual results

• There's a flash of the page on the layer below the modal

Environments observed

• Browser version: multiple including Safari mobile for iOS 12
• OS version: multiple including iOS 12
• Device model: multiple including iPhone
• Device language: Spanish

Check any additional observations

See for example https://es.m.wikipedia.org/wiki/Inglaterra#/talk while logged in with AMC enabled

Developer notes

The issue was identified and fixed as part of T217102 which stalled and never got completed. The problem is caused by the fact that TalkSectionOverlay extends Overlay, and thus there is a delay while loading the code. I don't see a shortcut to fixing this other than taking care of T217102 so this is stalled on that.

Compare this (language overlay and talk overlay are both using composition:

mw.loader.using('mobile.talk.overlays').then( function () {
 window.location.hash = '#/talk';
setTimeout(()=> { window.location.hash = '#/languages'; }, 1000 );
} );

with

mw.loader.using('mobile.talk.overlays').then( function () {
 window.location.hash = '#/talk';
setTimeout(()=> { window.location.hash = '#/talk/1'; }, 1000 );
} );

where /talk/1 is associated with an overlay not using composition.