Error: file is missing, Promise has not been resolved (sometimes)
Hello,

Since upgrading from 8.0.2 to 11.0.0 (node 14), when uploading a file from iOS (tested on Safari, Chrome) or MacOS (tested on Safari, Chrome DOESN'T HAVE the bug), the file is sometimes missing as the Promise has not been resolved with its content.

I have now tested around 100 times on Chrome MacOS (100 worked), and around 100 times on Safari MacOS, Chrome iOS and Safari iOS (around 40 worked). When it did not work, the file is missing and only the `promise` and `resolve` keys are here.

I would gladly help you fix it if I can, would you have any idea where it may come from?