ModSecurity: Input filter: Failed to create temporary file

Running a cPanel server with ModSec. Trying to upload media to WordPress, any file larger than ~ 125KB is throwing a 404. In the Apache error logs, I found this being written on failed uploads:

ModSecurity: Input filter: Failed to create temporary file /tmp/mod_security/20160827

Disabling ModSec restores functionality, but I hate to do that and would rather figure out what the issue is. Looking in my tmp/ directory, it's nearly empty with only the mysql.sock file and an .ftpquota file.

Any thoughts on what might be going on here?

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