Could not load the preview image. Please reload the page and try again – error on image upload

In my particular case functions.php of my theme was involved.
Just remove empty space after end of "<?php /*code or comment*/ ?> "
There should be NO empty space between "<?php ?>" tags.

You can find more info: https://wordpress.org/support/topic/basic-image-editor-not-working/

Good luck!

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