"502 Bad Gateway messages" after clicking the "Login as a User" button

If you get a "502 Bad Gateway" message after clicking on the "Login as a User" button, follow the instructions below.

Navigate to the domain settings (Plesk or cPanel), via your hosting provider panel, go to the Apache & Nginx Settings and add the following in the box "Additional Nginx directives".

proxy_buffering on;
proxy_buffer_size 128k;
proxy_buffers 4 256k;
proxy_busy_buffers_size 256k;

or

fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;

This is a known issue on WordPress. If you are unfamiliar with editing the server settings, it's better to ask your hosting provider to do this.