Can't upload pdfs to WordPress, get server error

When I try to upload a PDF to my Media Library it either does nothing but show a frozen status upload bar or eventually it fails and gives me an error of "Unexpected response from the server. The file may have been uploaded successfully. Check in the Media Library or reload the page.".

Images seem to upload no problem.

I don't have much experience in this area but I do have access to the server via SSH. I just have no idea what to do to fix this. Any help is appreciated.
I actually tried images and those don't always work either. The weird thing is that it's inconsistent. Sometimes it works but other times I have to try 3+ times before it will eventually upload.

I don't think that it's my internet connection as another web administrator is having the same problem with the site.
Here's what I've done so far:

File permissions seem fine. Relevant folders:
wp-content 755
plugins 755
uploads and all directories within 755
.htaccess 644

I installed the WP Health Check plugin which runs the site with all plugins disabled and the default theme and uploads still did not work.

Where is the error log that I should be checking?
The error message has now changed to this:
"Post-processing of the image failed likely because the server is busy or does not have enough resources. Uploading a smaller image may help. Suggested maximum size is 2500 pixels."

After trying this particular upload, the error log in usr/local/lsws/logs has these new errors:

Connection idle time too long: 301 while in state: 6 watching for event: 8452, close!
Content len: 463110, Request line: POST /wp-admin/async-upload.php HTTP/1.1
HttpExtConnector state: 10, request body sent: 0, response body size: -2, response body sent:0, left in buffer: 0, attempts: 1.

But I don't know what this means or how to fix it.


You can log a ticket with us, with server root ssh login, your wordpress admin login, and your image links failed to upload and steps to upload the image, we can try to reproduce it to see any errors. To me, it is more like a php error, not OLS error.