I will be the first to state the obvious workaround ... save your project and shut down arcmap before locking.
Now there must be reasons that users need to leave a project open and lock there computers, but I can't replicate it as the administrator on a standalone installation of 10.4.1, not connected to any server stuff at all, and McAfee virus scan.
So... is this a standalone installation?
connected to any server for data etc?
virus scan?
limited permissions?