Hi @appeffie,

It sounds there could be two things related to this issue. The first thing that popped in my mind while reading your question was the max execution time being hit.

Additionally, what other it could be is some issue with Nginx itself which is being hit on certain condtions.

Luckily, since you are getting 504 Bad Gateway both errors should be logged in your Nginx error_log. I would recommend checking your error logs like so

tail -f /var/log/nginx/error.log

Once you’ve executed the command, try to re-upload the file. The error should be logged in as soon as you see the error on your website.

As soon as you see the error, you can post it here and we’ll be able to provide you with more information how to proceed.

Regards,
KDSys