Downloads for PDF file are failing

My customers are complaining it is failing to download – I’ve always had this problem from iPads/iPhones but recently upgraded from WordPress 3.9 to 4.2.3 and I seem to be getting many more complaints. They seem to complain that it starts to download and then says that the file is broken…

So far I’ve heard people complain it fails to download from:

iPhone
iPad
Kindle Fire
and Mac

but the links work fine on PC via Chrome browser. I was looking into what the response headers were and I get the following (Note this is from a working system):

Response Headers:

Cache-Control:must-revalidate
Connection:Keep-Alive
Content-Description:File Transfer
Content-Disposition:attachment; filename=OhSheGlows_RecipeBundle.pdf
Content-Length:35524579
Content-Transfer-Encoding:binary
Content-Type:application/octet-stream
Date:Tue, 28 Jul 2015 15:27:31 GMT
Expires:0
Keep-Alive:timeout=2, max=100
Pragma:public
Server:Apache
X-Content-Type-Options:nosniff
X-Frame-Options:SAMEORIGIN
X-Robots-Tag:noindex

Request Headers
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Encoding:gzip, deflate, sdch
Accept-Language:en-US,en;q=0.8
Connection:keep-alive
User-Agent:Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.134 Safari/537.36

I’m curious if I should be seeing the following?

Content-Type:application/pdf

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