W3TC, downloadable products, X-SendFile and mod_fcgid: stderr: PHP Fatal error:

Hello to everyone,
I’m trying to figure out why the requests to Woocommerce downloadable files (zip files) end in a white page. This happens only when the file is quite big. It happened even if 30 mb files too and so I increased php memory. At the end this can not be the solution. I’m on centos 6.5, fcgid, xcache opcode and x-sendfile mod installed to serve the files.
Apache log when requesting says: [warn] [client x.x.x.x.] mod_fcgid: stderr: PHP Fatal error: Allowed memory size of 1585446912 bytes exhausted (tried to allocate 656494407 bytes) in */wp-content/plugins/w3-total-cache/inc/define.php on line 264

When w3 total cache is enable (even one only among the caches type) it looks like i’m caching the links to downloadable files, this type of links
/?download_file=3243&order=wc_order_543c74075d790&email=customer%40email.com&key=fc53bedbb37e9581057aefef59957218
I could not find a way to exclude this string from being cached.
When i disable w3 total cache i can even download 10 gb of files, with 128 mb php memory limit.
Any solution? I would like to keep w3 total cache.

https://wordpress.org/plugins/w3-total-cache/