RecyclerView is scrolling to top, while user is scrolling down (bad anchorPosition?)

After continuously scrolling down, after a while RecyclerView is switching his position to some element which was before, resulting in not smooth displaying of elements in it.
I only change NETWORK_PAGE_SIZE to 20, and switch to latest versions of:
roomVersion = '2.4.3'
pagingVersion = '3.1.1'

I added logs to `GithubRemoteMediator`, when scrolling down, there is:
```
15:21:54.884 RemoteMediator D load, type: REFRESH, state.pages.size: 0, anchorPosition: null
15:21:55.935 RemoteMediator D load, type: PREPEND, state.pages.size: 1, anchorPosition: null
15:21:55.999 RemoteMediator D load, type: APPEND, state.pages.size: 1, anchorPosition: 3
15:21:56.918 RemoteMediator D load, type: APPEND, state.pages.size: 1, anchorPosition: 0
15:21:57.748 RemoteMediator D load, type: APPEND, state.pages.size: 1, anchorPosition: 0
15:22:02.064 RemoteMediator D load, type: APPEND, state.pages.size: 2, anchorPosition: 40
15:22:04.697 RemoteMediator D load, type: APPEND, state.pages.size: 2, anchorPosition: 30
15:22:08.322 RemoteMediator D load, type: APPEND, state.pages.size: 4, anchorPosition: 81
15:22:10.000 RemoteMediator D load, type: APPEND, state.pages.size: 2, anchorPosition: 41
```

As You can see, anchorPosition after element 81 is going to be 41, which result in RecyclerView most likely going to that element.

Start by reproducing the issue in the codelab while continuously scrolling down, then inspect the GithubRemoteMediator load logs and the reported anchorPosition changes. Determine why anchorPosition moves from 81 back to 41 and verify that scrolling no longer jumps to an earlier element.

Written by the indexing model from the issue text.