When leaving a file explorer window open on a mapped drive it can randomly close, this can be due to the mapped drive setting in GPO configured to replace as shown below.

When the GPO runs a background update this can lead to the file explorer closing as the mapped drive is replaced, this can also cause issues with files that are open by applications in the background.

The solution to prevent this from happening is to change the Action in the mapped drive properties to Update within the GPO Policy.