File upload selection disappear when form validation kicksin

I'm thinking that your validation could be a postback, and it could be a good reason why the files aren't kept. 

 

Or another thing, it could the logic within your validation. I'm not really sure what's happening within your validation code, you might have called the form.reset() function that's why again the files aren't kept. 

 

Another guess, store the previous files into localStorage then retrieve that storage when you want to submit the files to the server. 

 

Cheers, 

Jin