Posts viewed in the app reader persist even when deleted

Expected behavior

When a post appears in the reader but is subsequently deleted, it should also be deleted from the reader view.

Actual behavior

When a post is viewed in the mobile app reader but is then deleted from the source blog, it remains visible in the reader.

Steps to reproduce the behavior

1. Publish a post.
2. View the site's feed in the mobile app reader and find the post.
3. Delete the post. I deleted from within the app, but I don't think it matters.
4. Refresh the feed in the mobile app reader. The post remains.

When I tested this, I checked that the deleted post that persists in the reader is deleted from the web reader's stream, even if it has been viewed in that stream previously. So I do not believe that this is an issue with the server-side feed being cached.

A user reported the issue, and I cannot reproduce for their site. The post they're still seeing is from April 9. They reported the issue initially on August 30 and sent screen shots showing a deleted post still displayed in the reader. When I load their site in my reader, I do not see that post. So I wonder if it has to do specifically with caching in the app of posts already viewed. The user confirms that the issue appears only in the app reader.

I also unfollowed and followed the site a couple of times from both within the reader and within the web app, and this didn't cause the posts to be removed from the reader view. But, when I re-follow and view the site feed itself within the app (from the "Followed Sites" tab), the deleted posts do not appear. But, further (I just kept trying things), if I add a post, view it from the single-site feed under the "Followed Sites" tab, delete it, and then try to refresh that view, the newly added and deleted post also persists.

It seems like the main feed view and the "Followed Sites" single-site feed view can get out of sync and that the mobile app is caching data that no longer lives in the feed itself.

#2311337-z and follow-up #2362592-z

Tested on Pixel 3, Android 9, WPAndroid 13.2

Start by reproducing the described flow in the Android app reader: view a post, delete it, and refresh both the main feed and the Followed Sites single-site feed. Compare those views to determine where deleted posts remain cached; done when deleted posts disappear from both views after refresh.