OAuth logging in isn't closing my WebView in the app

(I wasn't sure how to re-open a ticket, so this is a follow-up to #10725 - I updated my Rocket.Chat server to version 0.64.1 and am still having the problem.)

I made this video to show the issue, seemed easier than describing it:

https://youtu.be/ybZQQjdy6jE

Description:
When logging into the mobile app of Rocket.Chat, I use an OAuth through WordPress.

If you try logging into Rocket.Chat and are not yet logged into WordPress, there is a bug. The popup brings up your WordPress login page, but after entering your login info in WordPress and logging in, the WebView doesn't close. A new user ends up inside the WordPress site, as opposed to being sent back to the app.

If you're already logged in to the WordPress site, and then you try to login to Rocket.Chat using OAuth, then it works properly.

Server Setup Information: Version of Rocket.Chat Server: 0.64.1
Operating System: Android
Deployment Method(snap/docker/tar/etc): Heroku
Number of Running Instances: 1
DB Replicaset Oplog: enabled
Node Version: not sure where this would be listed
mongoDB Version: I'm using Compose.Io
Scope: openid
Token Sent Via: Payload
Login Style: Popup
OAuth Setup: CUSTOM (the regular 'WordPress' one has never worked)

The issue names no source file or test. Start by reproducing the custom WordPress OAuth login in the Android app with a logged-out WordPress session, then trace the OAuth WebView flow and its callback handling. Done means the WebView closes after successful login and the user returns to Rocket.Chat instead of remaining on WordPress.