I have several courses which when i perform a restore to new course cause Moodle to hang for ever, I have to close the browser down. When i log back in the course just says that "course restoration in progress" and no content has been restored apart from empty topics.
However if i deselect enrolled users it works fine, I then can merge the course from the same backup and deselect activities and resources and this then puts all the uses back with no problem.
But it won't work as a whole package restore.
Moodle 3.1.2 (build 20161020)