When doing a Bulk Copy, more often than not, I am receiving the time out error message. I do not walk away from my machine, if anything I am doing other things on my other monitor. When I check the history logs, it looks like the bulk coping was successfully executed.
The error occurs because there has been a break in the connection between the browser and Anaplan. The browser tries to maintain communication to the server through regularly asking for status updates, you may see these as blue popups or "toaster" messages, or through a progress bar on an action or process. This drop could be a loss of network connectivity, such as a brief wifi drop out or it could be a network timeout; some proxies or firewalls may only allow connections for a specific amount of time. Check with your IT department and they may want to setup network tracing if they can't immediately identify the reason.