In the new HTML5 Designer, if a user closes the web browser without deploying the workflow or selecting File - Close, the workflow will remain Locked out by that user.
These changes are being tracked in [Designer].[Process] table via CheckedOutBy column.
There is an existing Feature Request for this which you can upvote here: https://ideas.k2.com/ideas/APIT-I-336.
The current workaround is to change the CheckOutBy and Owner and will require direct database modification.
Do not modify any database definition or database content unless specifically instructed to do so by K2. No changes to the K2 Database definition or content are supported unless specifically instructed by K2.