Had the same error on local environment.
The error was due to an nginx permissions error.
Running this on macOS with local brew services nginx.
Local dev env
brew services nginx, php7.2
Error in the /usr/local/var/log/nginx/error.log file was
[crit] 7566#0: *31067 open() "/usr/local/var/run/nginx/client_body_temp/0000000035" ...