Files not uploading on mobile

I have a form with a file field and an upload action. It is working on desktop - the file is successfully uploaded to my server.
​
It is NOT currently working on mobile, for myself and for one other user so far.
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I'm on Chrome on Android, other user is iPhone
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Here's the relevant debug section

Array ( 
  [upload73] => Array ( 
    [path] => /home/...path.../onboardingContracts/tmp/ 
    [file65] => Array ( 
      [extensions] => Array ( [0] => jpg [1] => jpeg [2] => png [3] => gif [4] => pdf [5] => doc [6] => docx [7] => txt [8] => zip ) 
      [saved] => 0 
    )
    [var] =>
  ) 
  [switch51] => Array ( 
    [finished] => 1 
    [var] => NO
  )
)

Also not working on Macbook. Working on my Windows 10.