Large File returns Error 500

Hi,
I noticed that downloading a big file uploaded in the “private files” section fails with an error 500 (I checked my hosting LOG but no details are provided).
The very same file with another plugin (download manager) downloads with no problems, so it shouldn’t be something by the hosting. Anyway, as I checked on previous support questions, here’s my phpinfo output for relevant entries:
memory_limit 512M
output_buffering 4096
post_max_size 64M
upload_max_filesize 128M
max_input_time -1
max_execution_time 300

Again, on a different plugin it works (I also checked both source codes and tried to have them match when handling the file serving but had no luck).

Any suggestion?