Post-processing of the image failed likely because the server is busy.

This was a hard nut!

We got this error with a LiteSpeed server running a WordPress site.
Trying to upload an image resulted in the error “wordpress image upload error: Post-processing of the image failed likely because the server is busy.”

Adding the following to the site’s “.htaccess” resolved it –

<IfModule LiteSpeed>
SetEnv MAGICK_THREAD_LIMIT 1
</IfModule>

* This is effective for LiteSpeed servers only