When editing a profile in the JCE component area, whenever the profile is saved/closed/checked out, the error "Column 'checked_out' cannot be null" shows, and the only available option after this is to return to the dashboard.
Any changes to the profile I've made have been saved successfully even with the error message. No other issues spotted when using the editor in articles. When editing the table in the database, the 'checked-out' value of the edited JCE profile was that of my Joomla user ID. Changing this value to 0 checked out the profile in Joomla.