Slow thumbnail loading time when selecting media via the image block vs the media library

Expected behavior

When loading the media library to upload images to a post, the thumbnails would load quickly similar to how they do in the browser.

Actual behavior

When your images are large and you have a lot of them, you'll see a significant delay and on some connections, the thumbnails don't load at all.

Steps to reproduce the behavior

I was able to replicate it in the user's site (Blog Upload Space: 45.4% used of 6.144MB), but not on my test sites. The user reported the images don't load at all for them on an average 4g internet connection or 12mbs. Using a 180mbs connection, the image thumbnails take a couple of second to load each time you scroll down further on my end.

The specifics I noticed here are that the images in their media library are quite large (most around 3MB). They have 2.7GB of media space used up on their Personal plan site (WordPress.com).

The user reported this happens when they go from the Image Block to add media from the WordPress Media Library to a post, but not when they try to open the media library directly.

Steps:

1. Go to My Site > Blog Posts and create a new post.
2. Add the Image Block and select media from your WordPress Media Library.
3. Scroll down to load images on a site with a heavy media library and large images.

Internal report: 3675476-zen

Tested on Samsung S9+, Android 10, WPAndroid 16.5-rc-3

This sounds related to https://github.com/wordpress-mobile/WordPress-Android/issues/13224 but, I opened a new issue since the other one is specific to videos.

Start by reproducing the delay in the Android app through My Site > Blog Posts, the Image Block, and the media library, then compare it with opening the media library directly. Test with a large, heavily populated library like the report describes; done means thumbnails load reliably without the reported scrolling delay or failure on the stated connection conditions.