Now that I have your attention, this might be a blunt statement, but it's intrinsically correct. Whenever you make an user download a file, you need to warn about the possible consequences.
As you know, mobile downloads are a beast of its own, and they have rules that don't apply to desktop. They're also affected by:
- Data Transfer
- Device's Storage
between other. Your user might cover all of the above, and sometimes they don't. Even the same user on the same device may have different conditions at any given time.
The Productivity Side
Size limits, no matter what device you use, have to account for the specific needs of users. If your admin needs to create a 10Gb document, how are you helping your user by limiting the size to (say) 10Mb? Just imagine telling the user "sorry, we'd love to let you do your work but we can't because we decided a file size and stuff". Again, a blunt simplification, but this is what will happen
Solution: Give control to your users
Simply let your admins or power users upload the files to any file sharing service (Dropbox, Drive, etc) or even create a bucket or download page on your site for download on demand. This way, the end users will decide when and how to download your files. And this time, the files might be of ANY SIZE. Simple and straight to the point.