Reader: unable to 'mark all as seen' when posts are received via the 'x new posts' button

[bluefuton]

Steps to reproduce

1. Starting at URL: https://wpcalypso.wordpress.com/read/
2. Wait for new posts to be published
3. Click on the 'x new posts' button

What I expected

I can 'mark all as seen' even if the posts arrived via the 'x new posts' button.

What happened instead

The button is greyed out when I receive posts via the 'x new posts' button.

Screenshot / Video

cc @unDemian

[github-actions]

This issue is stale because it has been 180 days with no activity. You can keep the issue open by adding a comment. If you do, please provide additional context and explain why you’d like it to remain open. You can also close the issue yourself — if you do, please add a brief explanation and apply one of relevant issue close labels.

[davemart-in]

Closing as stale.