Large download product file is randomly truncated to random size, but sometimes not.

The original file is a 616MB video. When it’s downloaded it will sometimes work flawlessly but other times it only downloads a portion of the file, sometimes as low as 100MB. The incomplete downloaded files will play but only to the extent of which they were downloaded.

Any idea what’s causing this inconsistency and how to correct it?

PHP info for this server can be seen here:

This is an extension of this problem, which has been resolved: