I'm getting a 504 error while entering an attachment for a form

I'm getting a 504 error while entering an attachment for a form,it happened on April 6th and then again today 

Please provide us ID of the form that is causing mentioned issue. If the form is embedded, please provide us URL of your website, so that we can test your form there. 

Also are you getting a 504 error message, when you upload a file to your form or when you try to submit your form? Which file type are you trying to upload?

Looking forward to your reply.