When you open the "Add Media" tab in WordPress, instead of images, we see an infinite download scroll and a blank screen.
Also, this error, when loading the image, will lead to an error of the form:
img 2019-10-27 at 20.44.18.jpg
An error occurred in the upload. Please try again later.
It all looks like this:
How to fix
We need to find a reason that breaks the download. In my case, the PHP code was not commented out correctly, which affected the performance of the image loader. But the reasons can be any other. To find the error, open the console, tab Network. We reload the page and find (via search) a file async-upload.php. On the right, open the tab Response. And in this tab you will immediately understand (generally have to guess) what the problem will be.