Infinite scroll not working at all on simple and atomic sites

[mrsjaved]

Steps to reproduce the behavior

1. Make sure you have more than 9 posts.
2. Go to Settings -> General -> Writing
3. Enable the Infinite scroll under "Theme enhancements"
4. Now visit the posts page (either blog or home) and scroll down.
5. It only displays older posts button.

What I expected to happen

It should load more posts automatically at the end of the page scroll.

What actually happened

It only displays the load more button.

Context

Sorry if it's a duplicate report but I could not find a relevant issue except this one from bugomatic: https://github.com/Automattic/o2/issues/201

It's very old and no one is assigned to it yet.

Browser / OS version

Mac OS BigSur, Chrome Version 91.0.4472.77

Is this specific to the applied theme? Which one?

No, I tested with multiple themes.

Does this happen on simple or atomic sites or both?

Both.

Is there any console output or error text?

No

Level of impact (Does it block purchases? Does it affect more than just one site?)

No. I have only seen one site where a user reported this issue.

Reproducibility (Consistent, Intermittent) Leave empty for consistent.

Screenshot / Video: If applicable, add screenshots to help explain your problem.

NA

Follow-up: 4044906-zd-woothemes

[synora]

I can replicate this as well. I seems like "Display # per page" setting in Content types is overriding Infinite Scroll(when enabled).

[kwight]

Hm, I'm unable to reproduce this myself on a Simple site.

[msilbers]

Just had this issue with a customer in 32654003-hc using the Rowling theme. It's also happening here on my test site using Canape, seems to be unrelated to which theme is being used: https://melissasgutenbergteststuff.blog/new-blocks/

I have 48 published posts and Infinite Scroll is enabled. The customer has 111 and it will not load more at all, but does seem to try.

With some digging in Slack, we found that our server is returning this for the customer site

{type: "empty", lastbatch: true}
lastbatch: true
type: "empty"

Additionally, when Infinite Scroll is disabled, it adds the Load More Posts button, but the button doesn't work.

[msilbers]

Also reported in 32653959-hc using the Oxygen theme

[rinazrina]

I got another one here 31525068-hc using Escutcheon theme. Follow up: 4443027-zd-woothemes

Update: apparently this is not related to the original post. The issue has been fixed for my user.