This fix worked for me a while back, give it a go.
If you are tired of trying all the "solutions" suggested around the internet to this infuriating problem, here is a foolproof method to get your images, videos, or other accepted file types into the WordPress Media Library: http://www.conferencesthatwork.com/index.php/technology/2017/07/how-to-solve-the-infuriating-http-er...
After trying a lot of different things - and almost considering doing manual FTP uploads - I found this solution that worked for me. It's just a simple addition to your theme's functions.php file.
Nothing else worked until this.
Yo can fix by adding these codes above your .htaccess file.
SetEnv MAGICK_THREAD_LIMIT 1
For alternative methods Visit this site