Do these images reappear if you scroll or otherwise interact with the page after hitting the back button? In any event, I'll need a minimally reproducible test page (or pages in this case) to see the effect in action.

https://docs.google.com/document/d/1gIxTtMXDW4ggoIJ-Ts1y33zlLX-ZeiCVg0EjbQszyFQ/edit?usp=sharing

Once you open that URL page in Chrome, we load a bunch of images using yall with the following settings:

       document.addEventListener("DOMContentLoaded", function() {
           yall({
               observeChanges: true,
               idlyLoad: true,
               threshold: 600
           });
       });

Then, just click on Sign-up on the top right corner.
Then click on the browser back button. At this point, we do not see any of the images we saw before.

I dont feel like it has anything to do with the idlyLoad issue.

Thanks for your help.

Try dropping the attached version in to see if this helps:
yall-2.2.1.min.js.zip

I need to test this more in other browsers, but when I use local sources in Chrome to test this on a local version of your site, it appears to work. It adds the subtree option in the MutationObserver option, which is what I think fixes this issue.

Hi malchata, Thanks for the updated file. I tried it locally, and it seems to fix this issue. I expect it will be fine when deployed. Will let you know if we see any issues. Thanks again.

Officially fixed and released as version 2.2.1.